Dedicated Line(s), One Line or Two?

We are renovating our NYC condo (in a 1960, 175 apartment building) and using it as an opportunity to run a dedicated line direct from the breaker box to the two-channel system (20 amp, 12 gauge wire).  The contractor ran the line (singular) as requested.  But now I'm reading that ideally we should have two dedicated lines, one for the digital source (CDP) and one for the analog components.  The problem is that running the one line took a lot of work, chopping wall channels, removing molding, etc., and the new line has already been closed in.  I could have it redone to add a second line, but it won't be easy or cheap.  (Obviously I should have done more homework sooner.)   Questions: How much "dedicated line" benefit am I giving up if I just stick with one line, and have two duplex outlets on that one line?   Put differently, having gone to the trouble to add one dedicated line, will I still get enough improvement, so as not to feel like a complete fool for not adding a second line?   Is there a material downside to having digital and analog both drawing power from the same line?  Any input appreciated.  
You will get great advice from experts who helped me. But first, what components are in your system and will it include cable TV?
Einstein Tube Preamp
Einstein Light in Dark, hybrid amp
McIntosh MEN 220 Room Correction
KEF Reference 201/2
JL Audio F112 Sub
I should add:  no TV, no AV.  Its strictly for the 2-channel rig.
Let me throw a question into the mix that may help. I have multiple dedicated lines but they are still affected by noise elsewhere in the household electrical system since, by code, they must still share a ground. So, I guess my question is whether having two dedicated lines will effectively isolate the analog side from whatever noise the digital side potentially creates. (I don't use digital in my system so I can't speak to that). Rather than breaking walls again (i've been there many times in different houses), wonder whether some high quality 'box' that plugs into your single dedicated line can help you isolate- something that some power conditioners offer. I don't use any power conditioning so I can't help you on that front either (though I do use an isolation transformer for my tone arm compressor and it effectively shields against a nasty spike over the system whenever the compressor motor cycles)- I doubt an isolation transformer will shield against digital noise- but my point is, using something in a 'box' that plugs into an outlet can work (and will save you some labor and plaster dust). Be interested to see what the real tech/geek/engineering squad here says. 
 I have 2 dedicated lines, both 20A.  One is just for my power amp, the other for my pre, CD, TT, and phono pre. I think it sounds great, but I have no idea what a separate line for the digital would be like and have no immediate plans to find out. I'll obsess about something else!
It’s’ when you add computer audio into your system that a second line is absolutely necessary. Computers generate noise through the power line.
I wouldn’t worry about a second line, with your system a 20 amp breaker is just right. If you had mono blocks, you might need a separate line due to high current draw.
Start listening to music and see how it sounds.

As they say, hindsight is 20/20. Yes, 2 dedicated lines, 1 analog and 1 digital will achieve much better isolation between the analog and digital components. Some power conditioners can also provide isolation as well, but IMHO, it can't be as good as separate dedicated lines.

What tls49 said .

But , as Whart said , it is not a cure all for noise . I have two separate

lines , on different breakers with isolated ground , but still get a little noise from my CD player . Very slight and can only be heard without music playing .

For the power aspect , it is a no-brainer ...2 lines ! I look at it as 'future proofing' .

Good Luck .

saki is right about possible noise from your CDP.  But rather than encour a great expense adding a 2nd line, see how your system sounds and check for noise on the power line. A dedicated AC line does not guarantee noise free power, since you're dealing with the outside power grid.

Power conditioning can lower the noise floor, so can high quality power cables. If the ARC CDP does add noise, there are ways to isolate it from the analogue components. 
2 lines would be best, but you have to weigh the added cost vs. how your system sounds now.
I agree with lowrider57, listen first and then, if it sounds good, simply enjoy.
Had you asked before doing the work, I would have suggested installing 3 lines at 20A each or, if total available amperage was a problem, then 2 lines at 15A (for amps) and one at 10A (for front end gear).  Having one of the outlets spaced a short distance from the other two, but still along the equipment wall, would have provided a nice option in the event you ever decide to switch to monoblocks.   I also would have suggested the three breakers for the audio lines be located on the same side of the electric panel.  Finally, I would have recommended using 10awg romex wire,  regardless of what your electrician says is "minimum" code for the breaker size.

1 + lowrider57. 

I am using two dedicated line conditioners, one for digital sources and the other one for preamp/power amps to great effect. 

Whitecap, I believe  you are fine in your situation with one dedicated line. Adding a second dedicated line probably is not worth the extra expense at this point. In theory a second dedicated line or a third is the way to go however in the real world it might not make much difference. In my home I have four dedicated lines running out of my sub box to my main system and when experimenting with the digital components I'm not sure that I hear a difference. I do highly recommend an audiophile quality AC outlet, if you do not already use one.

I take it you are still renovating. Is the breaker box in a utility room rather than in a living area? Because if it's in a utility room, you can use an isolation transformer between the box and your dedicated line, and use another circuit for the CDP if it's a problem.

Since isolation transformers can growl when they are doing their job, they really should not be in a living area.

I use three isolation transformers to keep noise to a minimum. It made high priced power cords obsolete - direct test in my system. Thus you kill two birds with one transformer - isolate your analogue system from the CDP, and also from the elevator and God knows what else. Not to mention, making high priced AC power cords obsolete.

Plitron makes very fine isolation transformers, suitable for medical equipment, and they sell directly to the public. Highly recommended.
Pretty clever there, Terry. Rather than using the transformer to isolate the digital side, use it to isolate the analog side from everything else via the dedicated line and plug the CD into a non-dedicated line.
It’s another visit from an electrician, but not a wall buster, and you’re recommending just a naked transformer, right, not a whole box with the bells and whistles (additional outlets, Faraday cage, breaker, etc).

Thank you, Whart.

I use naked transformers in an garden variety electric utility box. But it really depends on the local electric code, and the expertise of the inspectors, because some inspectors get bent out of shape unless its a finished, boxed unit. Plitron sells both kinds, certified UL etc.

If I were doing it again, I'd talk to the electrical inspector before doing anything. And I'd try to make him work for me, not against me. Experience teaches.

I just built a custom house with a dedicated audio room and put in 3 dedicated 20 amp lines terminated right were I'm placing my gear. It is much cheaper to put more lines in when being built than to have to add them later. 

Indeed. I had my downstairs remodeled two years ago and put in four 20-amp lines coming off an 80-amp subpanel. I use them all: one each for amp, pre-amp, and phono stage; then the leftover one for digital, etc. I even sold my RSA Dimitri. Everything just sounds better plugged directly into the dedicated lines (with Furutech GTX duplexes and cover plates). So, I’d advocate for as many as possible.
I learnt recently from that even large amps use 4 amps continuously at most. Some power conditioners provide transient power up to 50 amps which should be ample for most amps. These power conditioners also provide isolation from digital circuits. I see no reason to get second line. More lines you have can cause problem of inducing hum occasionally.
Big improvement noted when I added 2 more dedicated lines. One for each mono block and the third for DAC /Transport. 
giri  "I learnt recently from that even large amps use 4 amps continuously at most."

That depends on the amplifier. Regardless, it isn't the draw at idle that's as important as the maximum amount of current an amp needs. With large amplifiers, that can easily be 12 amps. 

I would add to the dedicated lines a unit that would provide power protection and conditioning by using something similar to or a Sola-HD, MCR Hardwired Series - Power Line Conditioning with Voltage Regulation. You would go from the panel to this and then to the dedicated receptacles. This is not cheap, but in Audio terms maybe it is, approximately $500.00 for just this piece of hardware.
My opinions again.

When selecting a device to filter your power, make sure that the output is better than the input from the wall. Not all consumer grade devices do that - or so I am told. Thing is, do they fix the problem you have? A computer uninterruptible power supply is great if you don't care about the wave form, but just need juice to keep a critical computer system up and running. Audio needs clean waveforms, and no DC. IMO. That's an isolation transformer.

Just put a 'scope on a voltage divider across the output. Get your retailer to arrange that. Any tech in the country can do it. The picture on the scope should look like the sine wave from a calculus text. Compare the picture from the device under test to the raw output from the wall. If the device isn't better, if it has jagged steps or other grunge, don't touch it, even if its free, unless your wall power is truly ugly.

If you can't test directly, a good rule of thumb is to use industrial grade equipment, or better. That stuff has to work - their customers are sophisticated enough to test it and demand it. I hear the difference, so I use it.

Just my opinion. YMMV

Should add, that for a motor controller (as in a turntable), it is a good idea to synthesize the waveform with a special circuit. But that is a very special application, and low power, and relatively low cost.

Many thanks for the helpful comments.  As it turns out, there would be just too much tearing out and redoing brand new soffits and walls, etc.  So, I am going to stick with the single dedicated line.  I will explore the various suggestions offered here.  In particular, Terry, thanks for the input about an isolation transformer, will consider it with my electrician.  
My pleasure, Whitecap. Good luck with it all.

I'm in Manhattan as well, and would love to hear your JL subs when your system is done.   I'm trying to decide as well what dedicated lines to install (I'm running off a single 20 amp right now). 
This thread has me thinking.   Since the digital (a dac only in my case) needs so little amperage, why not use the standard wall outlet with a small isolation device or power conditioner for that, essentially giving you two circuits.   I'm going to try that as well.   
Also I use an older ps audio quartet on my elaborate computer editing system (which also runs jriver for my stereo) just to try and keep it from polluting the condo's AC.