Controlling the volume is a huge challenge and only the best preamps can do it without losing anything in the signal.
With all due respect... that's not true. Audirvana has an excellent volume control. (Roon also). No preamp needed. It doesn't lose resolution as you turn it down so it sounds good at lower volume.
So the question is... what exactly is a preamp doing that makes it sound so good?? Adding gain. Colors the sound and, in the process, adds dynamics. Perhaps a bit of the Fletcher/Munson curve for better low level performance. Perhaps add tubes for some 2nd harmonic distortion.
Tests have shown that people, in general, clearly prefer this sound.
However, it seems a bit counter intuitive. We want to get the highest resolution music stream source and components with the lowest possible distortion levels. We seem to want the music as it was mixed from the studio but then add gain/distortion/color back via the preamp. Two steps forward and one step back!
Using Audirvana without a preamp, If so desired, I could add the Fletcher/Munson curve via EQ without adding any gain or distortion and achieve a much cleaner end result that sounds GREAT at low levels. The added dynamic "Magic" is there with no added distortion. Clean with added headroom.
To be clear... no signal should get gain/boosted in EQ. It's opposite. From zero gain line the 'Curve' is created by pulling DOWN the midrange frequencies. Nothing gets 'boosted' above that line. The bass and treble are in a more extended curve WITHOUT adding gain. IMO a much better way to introduce the Fletcher/Munson curve than boosting gain distortion with a preamp.
Boost it up with a preamp (which the signal DOESN'T need), adding distortion, then try to clean it up the best you can. No wonder a good preamp is so expensive.