I find some of the superlux HD668B vs HD650 comments disturbing:
I also happen to have Sennheiser HD650 so I'm not totally alien to higher quality headphones. While HD650 does have more air in their presentation (music seems to be "far") than Superlux, I still like the frequency response of Superlux more. HD650 has slightly worse bass and roll-off of highs is starting to get very obvious when you get used to more tonally balanced sound.
Call me crazy, but I recently packed my HD650 back to it's retail box on top of my bookshelf. Seriously thinking if I should sell them or just keep them for another pair of different sound.
Just sold my HD650's because of them. For 1/10th of the cost I've got (to my ears) better mid/high performance, separation of instruments/vocals, insight into music, clamping force (as in less for my BIG old head!!) and less worry about damaging them.
As good as the best? Not sure, but now I don't want to find out.
Bear in mind i could have had the superlux for less than 35$!