So I got my HD6xx in last week. Gave them 2 day burn in and used them since last Thursday after the burn in.
Not really blown away. First off, the clamp force was way too much. A little bending and it was tolerable, but still not the greatest. The pads are extra firm and not exactly my preference. I like a soft memory foam earpad, not a super firm normal foam earpad. The velour though was very nice. I was surprised it wasn't the lint magnet I was expecting it to be as black velour tends to be a lint/hair magnet.
The sound was a bit boring to me. Mids were clear and preset, nothing emphasized. Treble was clear, preset, and only slightly rolled off. Very nice mids and treble. The bass was anemic. I mean it was there, but nothing punchy at all. Bass sounded technical without being fun. I didn't hear any veil or extra warmth at all. The bass is on par with my m560 stock. Both are very anemic to me with bass. Neither are rolled off on bass, just that bass is very quiet and recessed to the background. EQing the HD6xx had the same response as the m560. Both could take nice levels of eqing on the bass without distortion to bring the listening experience up to nice levels.
My other real problem with the sound was the ho-hum sound stage. It was there, but just barely outside my head.Imaging was good, but sound stage was nothing compared to a few other cans I have with direct A/B comparisons.
Mine came with a single ridiculously long janky cord though. The box was nice at least. Those are my impressions of the HD6XX. I found the Sennheiser HD206s to be better sounding in my opinion. I didn't find anything horrible with the HD6XX, just nothing to make fall in love with them over other options I have.