tuga
Legal Alien
in this instance i would say it has to do more with instruments sounding like instruments. a recording sound more like an actual instrument than the playback of the instrument. one major difference I've noticed is in bass texture. lower notes have more detail in their tonality than before and by a large margin. the small oscillations/warbles of a string beginning and ending a note are more clear.
Well, you like what you like, possibly you prefer some signal-correlated distortion which enhances the perceived spaciousness and resonance of instruments, a sort of glow that you'd get if you were to increase the reverb.
Of course not knowing your equipment or room it is also possible that the valve amplifier is technically more transparent.