@orchardaudio and @atmasphere thank you for your comments and the link. I read them with an interest, they sound convincing.
Class D offers a way around that, by allowing for profound amounts of feedback that is very difficult to do even with modern devices in AB circuits! With such high amounts of feedback its possible to build an amp that is both low in distortion while relaxed and detailed better than the best tube amps. To some this last statement might seem a bit weird but the experience of amps with low distortion not sounding all that good is common. At this point (and take this from someone who has been at this over 50 years) I'm very convinced that tube power amps are on borrowed time.
This is a very strong and challenging statement, especially from a tube amplified producer (i appreciate it very much). I did believe in this a few years ago. Nevertheless, so far, as mentioned earlier in this thread, i did not find a class D amp that sounds as good as my 5 watts tube SET class A amp. Perhaps, Orchard and Atmosphere already produce such class D amplifiers...
@orchardaudio and @atmasphere, do you expect to have a further breakthrough is the design of your class D amps in near future?
I realized that i don't have an answer on the following (perhaps stupid, forgive me) question. Would it make a sense to combine somehow GaN transistors with Purifi modules in a single amplifier?