Atma-Sphere Class D… Amazing

I agree on point 1. Measurements ought to be much more accurate, They are currently so useless and sloppy. Ought to go to to a at least few more decimal places.  We can agree on this.  Or not.

Its a matter of whether the person making the measurements knows what he is doing and whether the equipment needed is available. If you want to know how an amplifier will sound look at these things:

Distortion vs frequency; for best results it will not rise

Distortion spectra at 1 Watt

Distortion spectra at -6dB of full power. This particular measurement is where SETs fall on their collective faces as this is where the higher ordered harmonics show up, causing the amp to sound 'dynamic'.

In the case of the distortion spectra the lower orders must always be of enough amplitude to mask the higher orders regardless of the overall amount of distortion. THD as a measurement usually tells you almost nothing and is a good example of Daniel Von Recklinghausen's famous comment.

Blushing, I was kinda jesting about point 1.  Testing equipment is of course more than sufficient, and Ralph's considered comment is important.

I would also point out that the transition from most tube amps to Class D amps is probably more challenging for owners than most. Most speakers that sound good to someone with a tube amp will sound different with most Class D amps. As they would with most SS amps that also tend to have much lower output impedance and are also capable of driving more speakers well. Given that, I still suspect most tube amp lovers will be more pleased moving to a good quality modern Class D amp than others. But still in many cases, a move from tube amp to SS amp is also likely to involve a speaker change unless the listener is able to make the adjustment. I suspect many cannot.

Perhaps the Atmasphere Class D amp, coming from a vendor known for their OTL tube amps, is a more natural path to Class D for tube amp owners? One that is less likely to make owners jump ship on speakers they selected to sound good with their prior OTL amps? That would make sense. Just guessing though...have not done the homework yet on the Atmasphere Class D.

In any case, it is not possible to properly assess any amp without also considering the speakers it will be driving. The best amp/speaker integrations will ALWAYS produce the best results. Nothing else is possible, though some amps will care less about what speakers are used than others.

I would also point out that the transition from most tube amps to Class D amps is probably more challenging for owners than most. Most speakers that sound good to someone with a tube amp will sound different with most Class D amps.

Most loudspeakers are meant to be driven by a voltage source which is an amplifier that either doubles power as the load impedance is halved or cuts power in half as the impedance is doubled (tubes, if acting as a voltage source, do the latter and this does depend a bit on which tap is used on the output transformer).

A small number of speakers, but significant in high end audio, are meant to be driven by amps that behave more as a power source rather than voltage source (SETs are an example). The most likely embodiment of this is a tube amp that runs little or no feedback. Some of these speakers have level adjustments (meant to allow the speaker to be adjustable to the voltage response of the amplifier) on the back, like my Classic Audio Loudspeakers. If these adjustments are present they will have to be set up correctly but the speaker will accommodate both types of amps. Another example of this is the Sound Lab electrostatic.