Many research shows that high-end amplifiers no matter what type or the class are , have a level of sound quality that no difference in sound can be heard in blind test.

Important features are flat frequency response +/-0.2db irrespective of load impedance and low and frequency independent distortion behavior. THD and IMD distortions should be minimum 0,01% in whole frequency spectrum 20-20kHz at power range from 1W to half of maximum power of amplifier.

Regardless of whether it is tube amplifier or solid state class AB, or class D, blind tests show that listeners can not recognize which amplifier the sound is coming from.

Differences that we hear between  amplifiers which are not high end are audible distortions which are normally higher then above mentioned.

There are blind tests and double-blind tests. Blind test means that listener does not know which amplifier is playing, while operator who switches amplifiers knows which amplifier is playing.

Double blind test means that neither the operator nor the listener knows which amplifier is playing.

One of the best articles about double blind tests of high quality amplifiers you can read here:

https://audioxpress.com/article/differences-in-amp-sound-how-do-we-find-the-truth

https://audioxpress.com/article/differences-in-amp-sound-whats-the-truth