As I said earlier, I've kind of gotten over my early adult, 1970s slavish devotion to
numbers when it comes to hifi, but given a career as an analytical scientist, I
do kind of have to believe that most if not all important parameters can
at least in principle be measured. I don't think the "hifi" community has
yet figured out what those parameters are (other than the crudest and - not coincidentally - easiest to measure such as harmonic distortion, signal to noise ratio, bandwidth, square wave rise time, frequency dependent phase shift, etc.)
or how to measure them.
This being said, I think that
Stereophile (i.e., John Atkinson) bless his/their hearts, does a good job of testing amplifiers
objectively/quantitatively and (more to the point) does a good job of
representing the results with clear and cogent graphics.
If anyone reading this thread has never stooped to reading one, give it a go; how about this one, e.g.?
A fine "audiophile"-grade (for better or worse) amplifier from a gifted designer noted for clever and sometimes iconoclastic designs that produce excellent sound.
https://www.stereophile.com/content/pass-laboratories-int-60-integrated-amplifier
Read Herb Reichert's subjective review prose -- or not -- and take from it what you will... but, more to the point, read John Atkinson's prose and view the data in the
Measurements sidebar:
https://www.stereophile.com/content/pass-laboratories-int-60-integrated-amplifier-measurements
-- also read, and consider, Atkinson's summary statements in the
Measurements sidebar.