So,
I received my 680s yesterday, and I realize it's a bit early too write much about them because I haven't burned them in that much, but my initial thoughts are as follows:
Comfort: They're bigger than I thought they were going to be. In fact, they're a bit too big for my head - so comfort is still an issue, opposite of the S500, they clamp more onto the back of man jaw instead of the top of my ears. The headband is also a tad too wide.
Music: I prefer S500 for music - especially outside. Right now, the 680 doesn't make me feel the music as much as the S500 does. A lot of people have complained about the bass, but I find it actually a bit lacking in that department. Does that make me a bass head?
I'm not sure exactly what I miss in the bass right now, but I'm not getting the same ear massage from the 680s. Also, the S500s are quite up front while these feel a bit further away. Not just as engaging and hard-hitting. Vocals do come out very nicely however.
Gaming: They're very nice for gaming. Just tried some FFXIV and they had a better sense of space and placement. Very immersive. This point have been mentioned before, but I agree here.
They're not bad, but I don't find them super great either. Even if the sound gets different through burn-in, it won't solve the comfort issue.
I'll probably hold on to them for a little more though. I did give them to dad for a comparison and he clearly preferred the 680 before the 500, hm.
They're a step up from the S400 tho' - had the S400 sounded like these, I probably wouldn't felt the need to upgrade to the S500. So uh, not trying to derail the hype-train - just wanted to share my opinion so far.