How important is a preamp for purely digital sources?

I’m currently deciding if I need a pre-amp in my setup.
I’ll be using a Bluesound Node 2i as the source and a McIntosh MC7100 as the power amp.

the question is ... how much sound improvement will I get by adding a pre-amp knowing that all my source material will be digital? Will it be more beneficial if I add a quality external DAC instead?

I would put the money into getting a good DAC, since the DAC in the Node2i is nothing special.  Many DACs can be digital pre amps.  My personal experience 
was when my Mytek Manhattan DAC was doubling as a pre amp when the latter was having a minor repair issue.  I definitely preferred using it with a pre amp as I found the System had some glare without it, but ymmv.  Of course, many pre amp DAC combos are out there as well.  I would spend the money on a DAC now if the budget is small, and you can add a pre later if desired 
I was using ADI RME2 DAC as preamp (you always have some kind of preamp, passive or active, i suppose. If you're relying purely on digital volume control of DAC, that's the worst scenario since it reduces S/N ratio greatly. Try to avoid that at all cost!). 
Later I switched to tube preamp (Primaluna), and difference was significant. Another upgrade was replacement of ADI DAC, and that brought much more musicality, so go for R2R or mutlibit DACs rather than delta sigma ones (general advice, there are great delta sigma dacs of course!)

The knock against digital volume controls is no longer true.  If properly implemented they will not strip bits or increase noise levels when utilized in appropriate setups.
I agree with Hudo. I have a modwright swl 9.0 tube preamp and the improvement was stellar. Adding the Pontus dac a couple a years ago has made it hard to leave the house sometimes. If you do add a preamp, make it tubes. I have a solid state amp, and the combination of the two really sings.  
Check out the PS Audio videos on Youtube.
Paul McGowan give his take on this.
Here it is:
You need to tell us what your alternative is - **something** must do switching between sources (unless you are doing all that in the PC/whatever) and control volume. You may, or may not, requires a small amount of gain - its systems dependent (room, speaker efficiency, DAC drive level).
Digital volume control in any PC/MAC/whatever has serious issues that i wont get into here.  And they still exist.  Volume control within a DAC can be very good, or very bad.  In order to perform digital volume control in the DAC; it must operate on a roughly 30 bit or better native signal - some chips do this, others don't. ESS has a nice preso online explaining this and showing the numbers (which are scary). Roon's digital volume control is quite good, but even they admit its not on par with fixed volume. So its a trade-off.

I'll add one more comment since you used the wording "how much benefit?".  Components dont improve things.  A truly great components simply doesn't degrade the signal..... much. So you are really trading off the evils of the digital volume path vs the evils of an analog volume and gain path.  Conductive plastic vs digital manipulation and loss of resolution.
To give you an idea of the magnitude - were you to use the volume control in a mac or PC, you could easily get below 11 bits resolution, while audiophiles argue whether 16 or 24 are needed.  Holy orders of magnitude Batman!

If your solution does a pretty good to terrific job of digital volume control, and you don't have a really good DAC, I'd probably go DAC by the way - but the devil's int he details!
A preamplifier vs direct to amp to dac ,a good preamp always better especially a vacuum tube preamp it allowsbettrr dynamics 
soundstage depth as well as image depth .good power supplies 
and transformers give you the amplified dynamics ,
preamplifier it takes the signal and amplifies the signal.I have done many comparisons when I owned my audiostore ,as well as Audiophile consumer over my 40+ years in audio.
Enormously important!   However, there are not very many good preamplifiers on the market and the good one's are very expensive. 
Pinemoutain what do you base your comment on?
The answer is no. You seem to be fine as is , so dont drink the blue juice.
Check out a  Pre Box S2 Digital for a high performance good value DAC.
@pinemountainclub: there are plenty of excellent preamps available on the used marketplace - ranging in price from $150 to $10K + !
Improvement? Depends on how much your willing to spend. The Node works just fine as a preamp. The question of volume control was addressed on the Bluesound Forum a couple of years ago with the previous generation (Node 2):

"We attenuate and do not alter"

Here's a link to that short thread if you care to read it:

Underwood hifi is offering the Lotus DAC at a great price, including VC
I am seriously considering the rockna dac/preamp unit

All components have a value.  It comes down to how they work together to improve the sound.  Asking a general question like this will give you multiple answers from different member experiences.  Any old preamp may not be a benefit.  A DHT preamp may add wonders to the sonic improvement but how much and what you are trying to spend also can be a factor.

I have heard systems both ways and I prefer using a good preamp.  The sonic improvement to me was substantial in adding to the depth of the soundstage, clarity, musicality, micro to macro dynamics and back again, layering of instruments and vocals, and the piano and horns sounded "real" adding to the overall pleasant experience.  The direct way was not bad to say but the improvement in these and other areas was what I preferred.

Happy Listening.



+1 Schiit Freya, especially in tube mode. Makes MUSIC
i just started using the ifi itube as a preamp for my digital's minimalistic and cheap  for a tube preamp. you must use an external dac as well if you want proper sound quality(also try to store music on ssd drives,get the highest quality music files ,use a usb 3 port and a proper usb cable).a digital source needs a smooth sounding preamp to reduce glare and harshness  .an external dac will let you have more information and also affect the sound in a good way.
I have an MSB Analog DAC with a "stepped attenuation" volume control and power base, coupled with a PrimaLuna DiaLogue Premier HP.  I think that the combo sounds great and replaced my very excellent and modified Plinius pre.  Seems to me that logically and unscientifically, adding a preamp to mix just adds more "stuff" to the signal path.
I would like to suggest you examine using an Exogal Comet it’s both the a DAC and PreAmp.  It’s a SS DAC that many are using in combination with their existing Tube or SS Amps but it really shines when you combine it with Exogal’s Ion amp.  For more specific details check out Doug Schroeder’s Dagogo 2 or 3 reviews.  I have both Comet & Ion and knew in less than a minute of listening that it punches way above its price point and is a game changer sonically especially at its price point!
The Pro-Ject Pre Box S2 Digital is a great suggestion. It's excellent as both a DAC and digital preamp. To better this unit with a stand-alone preamp is not exactly cheap. I added an AVA Fet Valve CFR preamp between the Pro-Ject and amp. It improved the overall sound but for many, I think the margin wouldn't justify the cost. 

The Pro-Ject is one the best bargains currently available in digital audio. Dan Wright of Modwright Instruments was very impressed by it:
My experience is similar to Paul McGowan’s of PS Audio. I used to follow his mantra of “there’s no preamp like no preamp.” Paul’s opinion famously changed when he listened to an Aesthetix Calypso in a friend’s system. 

My experience has been similar with my BAT 51se. I get absolutely beautiful results when going direct from my PS Audio DAC to my Pass Labs XA30.8, but the 51se always adds something. 

Right now, I keep the preamp at unity gain, and do all of the volume changing on the DAC. I’ve resolved to sell my preamp several times in the past year, and put the money into other equipment. Every time I pull the preamp out, I miss the dynamics, the 3D imaging, and the richness that the BAT 51se adds. It doesn’t stay out for more than a couple of days.

Functionally, my DAC is the preamp. But the sound is improved through the 51se to such a degree that I just haven’t been able to bring myself to get rid of it, as strange as that may sound.
I've asked the same question and came to this conclusion - 
1) Is it necessary?  No.
2) Will it help improve SQ?  Very likely, assuming you pick the right one, which will involve time and money.  But it might not.
3) Most importantly, is is the best next improvement for my system?  Depends on what you're hearing and want you want to improve.  

Lots of good input based on others experiences, which can be helpful, but I think OP needs to share more specifically what their goals are to get the most valuable feedback.  

When I asked "what would a preamp do for me?" my conclusion based on forum feedback and my own research was to work on room treatments, isolation, power, and upgrade my source.

When I asked if upgrading my DAC was a good next step, my conclusion based on forum feedback and my own research was to work on power, consider different speakers, or to rebuild the XOs.  

This can be a strange and enlightening hobby, it's not all about buying a new black box.
I find a system sounds better with a
Preamp if you are going digital 
look into R2R Ladder Dac 
with a Jays Transport 

Well, oddly [to me, anyway], no one mentioned this, so I will ~ as observed, w/o a preamp, things do often sound a bit I use one w/an added feature: EQ. Several spoke of the preamp "adding something"...why not be more selective about what ~ and where, in the frequency range ~ you are adding? Or subtracting, when necessary...My C48 has 5 band EQ, which allows me to adjust for my room acoustics and system synergy...the only way I would ever relinquish it would be for a c52, which has 8 bands of EQ, rather than 5.  Purists, please don’t bother ~I don’t have a perfect anechoic chamber for a listening room, and if you want to be stuck w/whatever sound comes out, and that sounds good to your ears, great...I’ve done some room treatments, which help out, but it’s basically a crap-shoot and it is SO much easier, faster, and less expensive to make a slight adjustment to a few dials...and this way [unlike w/digital room correction], I can tweak to my room/speaker response/ears.  And, I’m using a Berkeley DAC, so I really don’t think I need EQ because my DAC is so poor...As a final observation, I find it interesting [and refreshing] that some of the writers of TAS, Stereo Review, and others are now swinging around the other way, and are openly in favor of a judicious use of EQ to enjoy their music, rather than viewing it as some anathema of evil to be avoided at all costs...try it, you might like it ;-)

I haven't used an active preamplifier since 2010, and I don't miss it, figuring that adding unnecessary circuitry to the signal path can only degrade the sound, especially if there's capacitors and op amps. I have a Luminous Audio Axiom 2 (a passive that costs $195). You get to remove  potentiometer from your signal path completely that way: the pot is shunted to ground, and a foil resistor is in the signal path. I found some of the responses amusing; about how people think their expensive preamplifiers add "depth of the soundstage", "clarity", "musicality", and "micro to macro dynamics". The DAC outputs are at the Redbook voltage level, and the signal doesn't need to be boosted any further before it gets fed into a power amplifier. There's usually two op amps in the output stage to convert current to voltage. 
There is another aspect to this entire discussion that has not been touched upon. While a preamp may be technically perfect and not enhance or degrade the sound there are two more links added to the chain with an external preamp that need to be considered. The interconnects. I have yet to find an IC at any price point that does not "color" the sound or add noise. I'm a firm believer in the concept of less (quantity not quality)  is more when it comes to ICs. 
jrapp, a well engineered integrated can solve that problem 
I know that but integrateds were not the subject of this discussion. preamp (s) are. When considering how important a preamp is (subject of discussion) and its effects on digital sources one must not forget the IC part of the equation. Years ago I added a very pricey and highly regarded BAT VK51SE to my then all digital system. I had used a pair of highly rated mid/high-line Audioquest ICs that I had from a prior system. The results were not as expected. The sound lacked warmth and was slightly muddy; that is until I replaced the ICs with Synergistic Resolution Reference Active series IC’s. The difference was astonishing; the expected tube warmth was now there and the muddiness was gone. This experience leads me to wonder if the results that some posters are touting are really the result of the preamp addition of the effects of the additional ICs.
Cables, are mostly snake oil, and differences are the most minute of any part of the audio chain, and are particularly small compared to those of the speakers. Don't understand why companies aren't being charged with fraud for making false claims about boutique cables. What's George Cardas new product now, the, "Cardas Clear Power Cable is George Cardas’ midrange Clear-series AC power cable.", which, "is designed for applications where you need a bit more current capacity and a higher degree of filtration than Clear M Power Cable, but you don't need a large, high-current power cable like Cardas Clear Beyond." Interconnect differences are inaudible for 95% of the general population if the connectors are clean and the wiring doesn’t add capacitance, or inductance. On the other hand, somebody would easily be able to tell that my power amp is on the warm side. If the system has EMI that happens to be picked up by the interconnects, then it's best to deal with that at the source. I have DH Labs Silver Sonic BL-1 Series II interconnects that I made myself specifically so I could make them as short as possible, and have heard zero difference compared to OEM cables, particularly with the short lengths that I use. It’s still available for $7 a ft on Ebay, and the ad says, "SILVER SONIC BL-1 Series II Interconnect is a high performance audio interconnect cable that combines the highest sound quality and reliability available at its price point. " Sure. Whatever that means. It's designed as balanced, and comes with a shield, but I don't use XLR in my system; my amp and sub can't do it. XLR had been designed for professional applications, to reject interference for the longer cables runs used in the field, and this could add little value to most amateurs.  People can reduce noise, by keeping cable runs short and away from noisy things like motors and VFD's. I have also used some BL-1 inside my power amp and that's the only place I’ve grounded the shield (it's a noisy power supply). You can use twisted pair cables to try and reject interference, but again, there's little of that in my system away from the power supplies. People can use ferrite beads or rings from Digikey to reject EMI in a a DAC or amp, or better yet, peel and stick foil. I have used it to try and keep power supply noise away from other parts of the circuitry. I can't detect how bad it is without an oscilloscope.

Take a look at a McIntosh D150 or perhaps a D100. My be a little bit more than you are want to spend but consider the axiom of buy it once and save in the long run.

I owned a D150 till I upgrade to a D1100 which I run now. The D150 will mate will with your Mac amp. Use the resonable S/PDIF out to the D150  from you Node and a decent set of analog lines to the amp. The D150 will perform volume in the analog domain. 

One thing that is rarely discussed with DACs is the analog output section. This is very import to the overall sound and vibe of the DAC (in this case digital preamp) and what works for one might not be a good choice for another. That said, since you have a McIntosh amp you might like the overall synergy from the two pieces. Also, if you want you can hook up other digital sources as well as a McIntosh CD/SACD transport where the DSD will be connected via a custom DIN connector. 

Very happy with my setup and the D150 seems to be going for around $1.5k to 1.8k these days. Find a nice one and be happy.
A preamplifier vs direct to amp to dac ,a good preamp always better especially a vacuum tube preamp

Any stage can only distort. You may liek the euphonic distortion of a tube preamp though, which is valid
t allowsbettrr dynamics
soundstage depth as well as image depth .good power supplies
and transformers give you the amplified dynamics ,
You cannot add dynamics (not without DBX like expansion). So this is false. maybe for some reason the poster gets the subjective impression of dynamics - louder maybe. We all know the Fletcher-muson effect. (e.g.: the loudness button!)

preamplifier it takes the signal and amplifies the signal.
Well, yea, superficially, but 99% of the time a preamp is actually delivering fractional gain (its only attenuating the signal).  If this were nto true you would nto have the option of driving the amp with the DAC at all!
obviously, if the DAC does nto have a high enough output level, you need a preamp.  I presume the OP knows otherwise.
What a preamp CAN do is fix impedance matching issues. if the DAC has a hgih impedance output, and the amp a low impedance input, you Will lose dynamics and a preamp might fix this. With well designed equipment this ought to be rare.

This is turning out to be very interesting ...

I'm currently at a stage where i'm still experimenting.  I've been using a 7.2 receiver for so many years and I want to explore a purely audio setup for now as I appreciate music more than movies.

The upgrade itch hits once in a while and I've been weighing if I'll be getting a pre-amp or a DAC and I'm leaning more into a pre-amp. 
Just a follow up question to the DAC ... it seems that DAC technology is constantly improving and there's a big possibility that a very good DAC today may be outdated in the next few years.  Is this the case? 
Interesting discussion. I've been running a modified Oppo 203 (digital only) to a Lampi Atlantic TRP dac, and then directly to ATC SCM19A floorstanding actives (and soon JL Audio e-110 subs). The ATC's are balanced but I'm using faux balance, i.e., unbalanced, out of the Lampi. Before the Lampi, I used a Directstream dac from the balanced ports for a few years. Since getting the Lampi, everyone I speak with, users and developers, say I'll get more out of it with a good tube preamp in there. Most of the ones I've been looking at are in the $3700-$4800 range new, which is out of my range at the moment (Rogue RP-7, Linear Tube Audio M3Z, Wells Commander, PrimaLuna Evo 400), so I've been eyeing eyeing PrimaLuna Dialogue's on the used market, which look like they can be had (with bargaining) for around two bills. I came across the Schiit Freya+ mentions today and read reviews and user comments, but I don't think it matches up with the PrimaLuna in any fashion except having XLR outputs and much lower cost. I should also say that I like a modestly warm (but not lush) sound, something emotionally engaging with the music rather than the "sound." Other suggestions or thoughts?