When we say we love the sound of tube amps, it's typically not just limited to the tubes. It's most likely in many cases to also be the output transformer, and obviously the speaker. At low volumes, the effect of the output transformer and speaker are basically negligible, IMO. You could basically end up with similar performance from a SS power amp. If you really want to exploit something sounding good specifically at low volumes, it will require that every part of the amp be designed differently from a standard amp design, which would probably also obviously include the speaker. Well, the other obvious missing part of this conversation is, what does it mean to sound good at low volumes? Some folks might think that your typical master volume amp, regardless of power, might sound good with the master cranked way down. Personally, I've never experienced one that I liked, unless the master was typically conservatively used. And IME, this stands for all of the typical flavors of pre-phase inverter, post-phase inverter, and the "cross-fade" MV. ...I've heard that power scaling can potentially sound really good at lower volumes, but I haven't experienced it myself. IMO, it's still probably a moot point, given that it costs more and is less common. You could probably get similar results using some other technology that is readily available and cost effective.