@moose89 There are now class D amps that don’t take a back seat to tube amps for smoothness and detail in any way. If you get the right one you may find that not only have you solved the heat issue but you may find you don’t want to go back to the tube amplifier. Its very probable that the class D amp will be lower noise too.
@jim2 If the feedback is deleterious to the sound, its only because the feedback has been poorly applied. This problem has been known for a long time (Norman Crowhurst was writing about this issue in the late 1950s along with the why of it) but oddly, few have come up with solutions. However the solution is pretty simple; I think tradition has been more of the problem than the feedback.
For example in a tube amp feedback is usually fed into the cathode of the input tube. That doesn't work (as Crowhurst explained) because the tube isn't linear. So the cathode of the tube causes the feedback signal itself to distort, thus causing it to not do its job properly. The solution is to mix the feedback with the input signal with a resistive divider network before the input signal reaches the input of the amp. Resistors are far more linear than active devices; in this way the feedback signal doesn't get distorted and so can do its job properly.
That's not the only problem, but its a good place to start if you want feedback to work.