I agree with @dave_b the audio performance on an amplifier, pre-amplifier or any audio reproduction gear should only be compared against how the musical instruments (especially the classical ones) and the human voice sounds at real concerts (preferably in a small venue/hall and without the use of any amplification that inherently induces harmonic distortions) sounds like.
During my youth I had the privilege to go to many live concerts in theater halls, jazz clubs, classical music concerts, etc) and I know how the instruments really sound. Once your ear is accustomed to those live sounds it becomes easier to distinguish audi that it’s reproduces through electronics and speakers and tell which ones are closer to the real sound than others.It always puzzles me that speakers/amplifiers/pre-amplifiers that add coloration and/or a certain degree of harmonic distortions, sound better to some people. This could very well be something they have "learned" by only listening to music from recordings or from live performances in large venues where the sound comes from large speaker systems and amplifiers anyway.
When you hear live music played on good piano, violin, cello, flute, oboe, timpani, cymbals etc. from close by and without any amplification, it will completely change your perspective on how music can and should sound.