Interesting report on the comparison between 90+ burn in and new. Don't know what to make of it. Probably would have a better idea if you did take note of how both sounded compared to each other before burning in the one pair.
For me, it seemed to take a LOT of burn in before they sounded good. I don't remember now, it's been a while since I've checked this thread, but I recall it was a very sudden change, and that it was something with more hours than you've already put on yours.
Still, I have a love/hate relationship with these cans. The last time I used them, it was in direct comparison to a pair of Audio Technica M50s and a pair of Logitech UE6000s. They were all driven by a portable FiiO E12DIY with OPA627 chips and BUF634 buffers.
The M50s sounded best, warm and communicative, with decent (but characteristically slightly flabby/loose) bass.
The UE6000 were alright, but more clinical and slightly lifeless, and didn't breathe as much as the M50s.
The S680 were horribly muffled and veiled in comparison. The did not sound awful, but so muffled in comparison to the other two.
Odd, because I've heard the S680 sound warm but open and lucid. Yet other times they sound really muffled.
Now I haven't really played the S680 for some time, so is it possible that these tighten up with disuse and need a little time to loosen up after sitting around? Crazy? Just a thought.
So I don't know what to make of it. Sometimes the cans surprise me with delightful sound, other times I feel like I should sell them.