It’s always been a matter of defining what “the threshold of audibility” is. The experimental psychologists have run double blind studies with samples of normal subjects, and come up with answers we audiophiles accept in principle, like a 3dB difference is certainly audible, and a 20dB difference is twice as loud, or that even a .25dB volume disparity will spoil the reliability of an A-B comparison in favor of the louder signal. Controlling for these errors with precision, maintaining the listener blindness, it’s rare that listeners can reliably discern many of the substitutions of cables or components unless one of them introduces a significant alteration to the signal’s integrity…
Even the ASR crowd fall into error by rating SINAD down to infinitesimally low levels. As if less than inaudible distortion or noise is somehow…less.
I don’t hear as well as I did when young, so my opinion means less now, but I can’t separate the profit motive behind commercial claims of superiority for whatever is being promoted from the verifiable evidence of that claim’s validity. People hear differently and no doubt some people hear better, but the lure of our hobby is mixed up with all kinds of extraneous factors besides what it takes for truthful sound reproduction.