Thanks for your impressions. I'd love to hear your set-up on the Bryston - and also get the chance to hear your 580s and compare them to my 600s. I have heard a lot of people say that the HD580 and HD600 are essentially the same - but after reading your comments I really do wonder.
As stated in my comparison (and the graphs/measurements actually show it also), the HD700 is definitely warmer and darker (than the HD600 at least). Where the big difference is (besides the bass) is in speed, and also the slightly recessed lower midrange on the HD700 and the elevated upper mids. They definitely can show more sparkle and excitement with some music - especially acoustic, or brass instruments - but the upper mids are so forward sometimes that it does bring female vocals ovely forward, and unfortunately sometimes can sound congested for my tatses (I have a lot of female vocal music).
Comparatively the HD600 does have more sense of space in my set-up - probably because the vocals are more balanced across the spectrum - and don't tend to sit as forward.
I've never heard the infamous "Sennheiser veil" - so it could be our sonic preferences at play
Nice to hear your impressions though - and I agree that for the right set-up and genre choices, the HD700 really is a very special headphone. Definitely has a sense of excitement and enhanced reality about it.