Break-in

I can't recall seeing anyone report that a component sounded worse after break-in. I'd say your suspicions are warranted.

But how do you predict how a component will sound after break-in, if you don't know what causes break-in? How does an engineer design for a phenomenon he doesn't understand? (Answer: He doesn't.)

As for measurements, I think Tom Nousaine once tested speaker drivers before and after "break-in." The differences were so small that they were swamped by the unit-to-unit differences. I would expect the differences to be even smaller for purely electronic devices.

I'm not sure I'd go so far as to say that the ear is the only "moldable" sensory organ. You can become accustomed to hot foods, rotten odors, even touching hot or cold items.

The point is that anytime you do a sensory comparison, the biggest variable in the mix is YOU. You can't hold yourself constant.

Sure, and when somebody compares mint and broken-in components in a blind test and identifies them consistently, I'll believe that break-in is a physical phenomenon. Until then, I'd argue that the psychological explanation carries a lot more weight