There's 1800 reviews for these. I suspect I won't say anything new with regards to sound quality and the spectacular sound- that's just a matter of history well documented at this point. But I will tell you this: put them into your source, play pink noise, and walk away from them for a week.
These headphones are GREAT. But you WILL NOT realize the greatness of them until the drivers are good and limber, and that's a function of time- they WILL get there. But until that time, you will very possibly NOT like them. There are engineers who dispute this phenomenon. In theory- okay-- yep, it sounds half baked. I will tell you, in praxis, those people haven't lived with these cans 1/4" from ones ears with no time on them, and if they had the misfortune of it, they would recant if they were educated listeners.
I did not like them when i got them. My first impression was literally 'These are broken.' I tried to like them casually listening a day or two, and was truly baffled. They weren't 'warm and midbass heavy', they weren't 'so relaxing I could fall asleep wearing them', they weren't 'thick and rolled off on top'. They were grating, upper midrange heavy, congested, bassless, and horrid. But- the story does get better.
So I set about running them 24 hours a day with pink noise.
Day 1, muddled. Crappy. Unlistenable still. Low bass, but no midbass. Grating. To get ANY bass, you have to turn up LOUD. ugh... so bad. Back on the pink noise.
Day 2-4- marginal differences- sometimes approaching nice. Sometimes just weird. Still grating and harsh, with very deficient midbass. Slightly less grating. Still has to be LOUD to have any weight to the sound. BACK AGAIN on the pink noise.
Day 5. What happened? Out of nowhere-- lush, heavy, black background, gorgeous treble that's unfatiguing, no upper midrange harshness. Midbass and bass filled in.
As I continue to listen to them, they continue to change two weeks in, and all for the better. Top end gets lighter, bass fills in... I really can't stress enough that the work to make these the beautiful sounding tools they are takes time, and it'll get there-- but spare yourself the first week of misery, and just find a download of a pink noise .wav and let it rip on loop while you listen to whatever you will inevitably replace with the 6xx.
i jest-- sort of. But it is a lovely can if you give it the time it needs to become something- and casual listening will take you forever to get it there on low volumes! Listen out of the fancy box at your own peril-- but for heaven's sakes-- if you find you don't like them-- don't give up on them and try it. I almost sold these after three days, and I'm very glad I didn't!