Digital gain vs analog gain

Digital volume control reduces resolution of the signal and is therefor depending on the original resolution of the audio file. With 24 bit you could  decrease the digital gain more than with a 16bit file  before you will lose resolution. As a rough rule of thumb  16bit files shouldn't be played with settings  lower than -10dB, 24 bit not lower than -20dB.

The analog volume control also does something "bad" to the audio signal. Normally it is a voltage devider circuit which shortens  some part of the audio signal to ground. Everybody knows that the volume control should be set at least around 11 o"clock or higher in order to get a good sounding signal at the output. The subtle information in the audio signal will suffer first if the analog volume control has to be set too low for comfortable SPL levels.

Ideally one would use a combination of digital and analog volume control: setting the digital volume control for full resolution of the digital signal and using the analog volume control as little as possible.

How effective one can combine these two settings depends of course also on the gain of the preamp, input sensitivity of the power amp, and sensitivity of the speakers. If everything lines up one could set the digital gain around -5dB, the analog gain to almost fully open and the SPL would be at 80-90% of full volume for loud listening.

There have been attempts to work around the neg. effect of analog volume control like putting the voltage divider after the input stage, using current instead of voltage control, or in the tube compartment one can use the 6386 (normally used in pro audio gear comressors)and control /adjust the gain instead of shorting a big amount of the signal to ground.

I need to be more precise: Using digital volume control  will reduce the original resolution of the audio file but it will only become clearly audible at some point (A/B comparison) compared to analog control. Those settings are -10dB and -20dB.

+1 @apogeum 

I think of digital volume control as the digital signal being altered which is something audiophiles seem to go to great lengths to avoid.

I think of analog volume control as signal attenuation which narrows the gap between the signal and noise (i.e. reduced signal to noise ratio) which is also not desirable in the next stage of amplification.

I think the pro audio rule of thumb for gain structure is to have the input signal as high as possible to maximize the signal to noise ratio (I might be saying this incorrectly).

With these things in mind, I would try to set everything to "zero" and let the preamp do its job.

This is one reason that I had a DAC that doesn't have any volume control and set my bluesound node to have a fixed output level.