Atmasphere class d amps can also be interesting. I did not find them on the site and have no idea on preferences made in their design. Neither i know if there are already completed models. Can Ralph provide more detail?
I can. Its been the most successful product entry we've ever had. We started shipping last June. We didn't put up the product page until about 2 months ago. Early on the project (about 5 years ago) we had a prototype that demonstrated that the idea was worth pursuit- and that a class D amp need not have any audibly objectionable characteristics.
The simple fact is most output sections in traditional amps have distortion product based directly on their linearity. And since the output devices are not all that linear, feedback has to be applied to make them look better on paper. That's been a problem in solid state amplifier design since the inception of solid state. Class D does not deal with that problem, since the output section does not rely on linearity at all- it switches. So the distortion generated has entirely different sources!
One problem in traditional designs is getting enough gain and bandwidth to support the amount of feedback used. Traditionally this has meant that the feedback at 100Hz is quite a bit different from what it might be at 3KHz or 7KHz and as a result brightness and harshness has been present (put another way, if there isn't sufficient gain and bandwidth in the circuit, the feedback will decrease with increased frequency).
We've all heard this over the last 60 years of solid state amps; brightness and harshness is for many one of the worst failings of any audio system!
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.
I play a set of our class D amps at home if that tells you anything.