Well I've been listening to them for a bit tonight (arrived today) and just some initial impressions...
1.) They look outstanding! Simply beautiful headphones. The photos don't really do them justice. The Bubinga wood looks outstanding.
2.) Yes they are heavier than either the LCD-3s or LCD-X, but on my head the differences are pretty small (though noticeable). Overall though, the comfort is about the same.
3.) Sound wise, they certainly are right up there with some of the best imaging for closed headphones that I've owned/heard in terms of air/space. Locating players in the sound stage is also very good; looks like the Fazor design is really helping in that area. The LCD-X / LCD-3 are a bit better, but they're open headphones, so not really a fair comparison. I'll try my TH-900s later and report back. But they are better at imaging over the AT W3000ANV, Ultrasone Ed.8, (previously owned both) and beyer T5p from what I can remember and based on my notes.
4.) Make no mistake about it, they have retained the Audeze sound with amazingly deep and textured bass, luxurious mids and treble that is never strident. They do have more bass than the LCD-3/X, not by much, but it's there. The treble seems a bit more forward than any Audeze headphone I've heard yet. But again, make no mistake about it, the HD800s, they are not! As mentioned, they have retained the Audeze naturalness of their other great headphones.
So far, colour me impressed.