I just got a pair of the Sennheiser HD-6XX and have been listening for a few days. The headphones seem very out of balance - most of the sound seems to be coming from the right cup. I did a reality check and switched the wire so the right terminal was in the left cup and vice versa, and the weight of the music was still on the right side. Then I did a reality check with my travel headphones (Bose Quiet Comfort 35s - don't judge - if you've ever been near a screaming child on an airplane you know how crucial a pair of these are) and did NOT notice the same phenomenon.
Anyone else have this issue? Did I just get a bum pair?