It was mostly the sluggish speed that drove me crazy. The delay when you clicked to play a track had a very noticeable pause too. It's an excellent device for sound, but as far as using it, they need a lot of work IMO.
Hmm... I actually found the M500 a bit bass shy, at least from memory. Maybe it was that lack of warmth. I don't know know how to pinpoint it exactly... I could tell they were quality headphones but the sound didn't pull me in. I'm liking my K545 a lot more. The Yamaha is interesting because I no longer have any open headphones.
I should probably wait until Friday anyway and see if any other deals suck me in!