From my relatively brief listen to the 800 it didn't gel with me at all, It sounded like it was lightweight, not much body and basically a nice, though bland phone. Comfort with the 800 was exceptional and better looking in the flesh than pics suggest. It was well extended at both ends but missed that 'certain something' and couldn't get me involved. The Audeze is completely opposite to that. Built like a tank, heavy and initially uncomfortable. The sound.. the sound! It is gloriously full bodied, very extended and very involving. They have a great way of sounding just right, natural and a much better window into the music. After just one day the comfort had gone from 'not very' to 'very good indeed'. The tight clamp is fixable with some careful headband bending, of course, be very careful if you do this, it only needs a little so it grips well instead of crushing your skull. Some have also complained about the adjustment ratchet, this too is easily adjustable with a small screwdriver to either make them adjust more firmly or even lock a position.
The new headband foam is also very good, exerting little pressure over the top, for my narrow head anyway. They are huge and the equally oversized pads help spread the load and I can now comfortably wear them for hours on end with no discomfort, even though you don't usually forget they're on your head. It's a lot of phone to try to ignore.