How to judge a preamp's sound

hilde

i would say that most high end preamps/linestages do have a distinctive tonality / ’sound’ that can be consistently heard -- even in driving a variety of amps

this can be in terms of tonality, drive/prat, grain/pixel size so to speak, size and depth of image, clarity/precision of imaging or lack thereof

of course there can be notable exceptions (e.g., signfiicant impedance mismatch, cabling complications...) but by and large, in my experience, this is true

 A reviewer usually uses equipment they are familiar with, not just throwing random gear into a review. 

you can hear tendencies in preamps that carry accross different power amplifiers much in the same way different phono preamps can sound  distinctive despite different turntables, cartridges and amplifiers. 
synergy matching is very important to optimize the overall sound.