A lot of the reasons why music becomes congested and distorted and compressed at moderate or louder levels have to do with things that go bump in the night, as your humble scribe has intimated over on the other loudness and congestion thread currently in play.
A lot of the reason are not (rpt not) related to the system per but to our perception (hearing) of the sound and the effect of the local environment on our sensory perceptions, especially the perception (hearing) of sound. You could say it’s mind-matter interaction. 🧠 It’s not physical or electronic. It occurs in the subconscious.That’s why this phenomenon occurs even when audiophiles are careful to address all of the usual (physical and electronic) suspects - you know, vibration, absorption, diffusion, break-in, fuse direction, cable direction, RF, sufficient power, time of day, etc.
“There is nothing wrong with your television set. Do not attempt to adjust the picture. ... We repeat: there is nothing wrong with your television set. You are about to participate in a great adventure.” (Outer Limits) 🤗