Reverse-engineering my speakers' API to get reasonable volume control

I know it is tangential, but this about his old system caught my attention:

  With that system, I could set the amplifier’s analog volume knob such that the max volume out of the streamer corresponded to my actual maximum preferred listening volume, giving me access to the full range of Spotify or AirPlay’s volume controls.

Assuming an analog input, this might result in a noticable quality reduction at low volumes.

Tangential fun fact: amps have a fixed gain, because it's hard to make a variable gain without distortion [1]. The volume knob doesn't control amplification, in fact it controls an attenuation stage, because it's easier to make variable attenuation with low distortion.

[1] that's why there were so many different "classes" of amps, they're all making different tradeoffs about how they're doing the amplification.