It always bothers me when some asks about a lower power tube amp and someone chimes in with, get a higher powered amp. To me if you want a 300b, 2A3 or 45 amp get one. I have all three. I listen to music all day and at good volume and one room is 1400 square feet. These amps are the best, and at the same time there is a culture around them. The people who espouse the more power mantra are not part of that culture and are irrelevant if you really want a low powered tube amp that’s about sweetness and musicality and tactile-ness.
@yaluaka I've tried plenty of SETs over the last 30 years as well as designed and built my own using the 45, 2A3 and 300bs. SETs do not rule the roost in any of the areas you mention above. But there are plenty of PP tube amps that fall short; if you've not been exposed to the right PP amps I can easily see how you came to your conclusion.
Here are some things to consider: The mark of the best systems is they never sound loud even when they are. You may have noticed that your SETs seem to get plenty loud but what is happening is the distortion they make causes them to seem louder than they are (there are sound pressure apps for smartphones that can easily show what is happening). When you have an amplifier with less distortion it will be very natural to use more power and enjoy it.
The distortion of SETs increases linearly as you increase the power level. Above about 20-25% of full power, the higher ordered harmonics start to show up. They appear on transients (where the power is) and because the ear uses higher ordered harmonics to tell how loud a sound is, this causes the transients to sound louder, giving the amp a very 'dynamic' quality.
IOW the dynamics of SETs is really distortion and nothing more- real dynamics come from the music.
Bandwidth is another problem; with greater power its progressively harder to make an output transformer that really has hifi bandwidth. So usually the highs are made right and the bass suffers, since the kind of speaker you need to really take advantage of an SET (likely horns) often don't have deep bass response. So if you really want to experience the music properly you'll need subs and driven by the preamp rather than the amps.
OTOH, there are PP amps that are every bit as involving that don't have these problems. Consider though that if you really want to compare apples to apples, the PP amp might have to use the same kind of output tubes, perhaps it should also be class A and zero feedback as well, to level the playing field? Usually these things aren't considered when making comparisons. You might also consider what happens if the PP amp makes the same power as the SET; for example if compared to a 2A3, perhaps the PP amps only makes 5 Watts? Again, to level the playing field.
If you work to eliminate these variables you find that SETs really don't have an sonic advantage over a well designed and built PP amp.