There are definite differences between amps and even from same manufacturer
I can refer to an auditioning of Vienna Acoustics Mahler using first Electrocompaniet AW 180, this combo didn't sound good at all... when switching to Electrocompaniet NEMO, it was like a totally different set of speakers, bass was clearly tighter and better and it sounded like lightning was coming out of the speakers... definite difference... there must however be something measurable that explains this, I thought it could be about output impedance but they're almost the same.... EC Nemo is actually bridged AW 180's so how could this be?
Nemo: Output Impedance (20 Hz-20kHz) < 0,009 Ohm
AW180: Output Impedance (20 Hz - 20 kHz) < 0,008 ohm
There are differences, but sometimes they may be in your imagination, sometimes not
But I'm not buying this that there will be no audible difference between the above mentioned amps, perhaps it's negligible, perhaps not....