I heard them during a meet, and it was only for a few minutes, but these are my impressions. They were terribly bright, detail was poor, the treble was a horrible mess, and the soundstaging and imaging was warped. How do they compare to the high end headphones like HD800, T1 (didn't really like the T1 that much either, although I admit it performed quite solidly), LCD2 and the like? They don't. In short, I didn't like them one little bit. Perhaps someone's magical uber amp might be able to fix those problems, but out of a VERY respectable WooAudio WA22, they were pure agony.
Sorry if I come out a bit too negative, but I really expected more out of such a beautiful headphone...
I was so worried at first that these would sound like pure crap that I had a hard time enjoying them at first. I kept listening for the "unnatural" bass, which I never heard, and the ear piercing cymbals, noticed but only here and there.
When I've had these recabled I'd be more than happy to let you sit down with them and just enjoy em for a few hours.
Time will tell if they'll come out on top, like the pro 2900's did for me.
Can't really listen to the opinion of folks who think Machine Head is something to do with an engine..