Not all evidence points to a root cause. Often we see something that on its own cannot explain how it works, like flapping bird wings. When man first struggled to unlock the secrets of flight, he assumed it was the flapping of wings—when in reality it is their shape.
When we hear differences in two amplifiers with similar specs, we can’t easily explain those differences. Some conclude what we hear cannot be correct. Others think specs don’t matter. Still others believe we just haven’t managed to measure the right metrics.
Imagine two amplifiers with identical THD (total harmonic distortion). One sounds better than the other. Upon closer examination, we see that there are hidden clues: slew rates, output impedance, headroom, linearity, levels of global feedback.
Just because we haven’t uncovered all the clues doesn’t mean they aren’t there to be found.