Regarding measurements, any decent audio analyzer can tell the difference between 0.001% and 0.002% THD+N, but I've never met a human that can.
There's also the "threshold of audibility" for any given audio imperfection. Some say that no human being can tell the difference between 44/16 and 96/24, but just crank up the volume during quiet passages and almost anyone can hear the difference in the noise floor.
We have measured amplifiers with amazing specs but "so so" sound, and I believe this is due to imperfections not covered by standard specifications, like control of a complex impedance with an arbitrary waveform (music). Can that be measured? Certainly, but understanding how the results translate to audibility is another issue.
So, at Digital Amp Co, we listen AND measure. There's no substitute for either. Without measurements, there's no real quality control for production, and no base guide for development.