Do Audiophiles usually keep the gain of the digital source at around 80%?

There are two things here. 

1. DACs capable of directly driving power amps obviously incorporate some kind of line stage (preamp) circuitry, allowing them to output the voltage required to do so. Without it, they wouldn't be able to drive a power amp any more than a turntable or a CD player can.

Obviously, the quality of that preamp section will vary from one DAC to another.

2. The position that preamps are obsolete and do nothing other than creating distortions is commonly shared amongst SINAD fanboys on ASR.

Audiophiles, however, almost universally agree that a high-end pre is an indispensable part of a well-thought out system.

If my limited experience in the matter is worth anything, I drove my monoblock amps with a DAC for several weeks while I was refurbishing my Krell pre. When the pre was returned to service, and the DAC moved behind it where it belongs, the sound quality improvement was very much significant.

I'm in the camp of those who believe that a great pre is a necessity. I also believe that a system's sound signature should be determined by the pre + amps + speakers system core, and that digital sources have no role to play in it. Just be neutral. You know what they say about too many cooks in the kitchen.

You don’t necessarily need a preamp, and I don’t wish to be contentious on this subject. However, a DAC with a well-designed gain stage—like the discrete Class A output stage in Harmony Micro DAC—can drive an amplifier beautifully. I used to be in the preamp camp for a while, but after getting a quality DAC like this, I’m switching back to the “no preamp is the best preamp” camp.

Inserting a good preamp in the chain can often sweeten the sound and augment the soundstage, but I also notice a slight loss in dynamics. I have actually mitigated that through the source by adding a DDC and good cabling. I believe the source dominates the quality of the signal chain, rather than the backend. This may contradict your statement, but I am simply sharing my experience.

Obviously the A8 has analog outputs because it's a dac/streamer, the volume control is in digital realm, it does NOT function as a pre.

The generalization of pre's as superfluous because it simply adds distortion, reduces dynamics, sweetens sound is absolutely ridiculous. I'm sure there are many here with quality preamps that find them indispensable. 

@lanx0003 

One thing we can agree on, I think, is that whether standalone or integrated to an amp or to a DAC, a preamp or preamp stage is always involved.

Sound quality notwithstanding, I have analog sources I need to switch, and I prefer discrete components performing single functions in my system; and finally, with very few exceptions, the best preamps are separates.

So, while a separate preamp makes the most sense for my own use case, that’s all preferences and there is no right or wrong answer.

Now I am sure some DACs are equipped with decent preamp stages, and I certainly don’t know every one of them, but I am going to have difficulty accepting that the vast majority of them are in the same league as high-end separates.

Finally, at the risk of being labeled a VC snob, I am going to have to respectfully push back against the notion that a digital volume control, even a 32-bit one, is an acceptable choice in any but value-conscious devices. Neither is a $15 Blue Velvet, by the way, despite the fact that those are original equipment in so many almost-high-end preamps selling for $2000 or $3000 or even more 

@sns  DMP-A8 features an R2R (resistor-to-resistor) volume control. This R2R (Resistor to Resistor) network, implemented with precision resistors and relays, is part of the DMP-A8’s fully balanced analog preamplifier section.  This says in the manual.  Where did you see that its volume control is in digital domain?  Did you actually own A8?