Generally speaking, I find claims that most headphones have major changes to their general character and tonal balance over the first few hundred hours to be somewhat specious.
I think, for example, when someone finds the bass level unacceptably low on a headphone, that this won't change enough in 1000 hours to make a big enough difference.
That if you put the 1000 hour headphone right next to one that was still in the box, and did a quick A/B test, neither would be found to be acceptable.
But over the course of 1000 hours, the owner is likely to get used to the sound signature and grow to appreciate it.
I've personally only witnessed a major change in a headphone due to burn-in, and it was a QP55x that had languished in a warehouse for 10 years before i bought it. The frequency response flattened out a bit, and it got more sensitive (louder) after I listened to it at work for 2 weeks.
But it still sounds like a QP55x, just, a little less peaky and a little easier to drive.
I think people underestimate how much their perception changes in response to the sound signature of a given headphone.
There have been people who gave it all up for a KSC75, but when i listen to my QP85 floats for 2 hours and then quickly put on my KSC75, the KSC sounds violently, evilly, corruptingly awful.
And yet an hour later, it sounds ok.
