Interestingly...the S2 did put my HD800S on the sidelines.... but my recent HD820, which I intended on using when needing a closed phone, have now done the same with my S2s (temporarily though
)....technically so far IMHO the 820 do have a cleaner driver, fuller sound and deeper and more authoritative base and relatively speaking a wide deep sound stage.
I've been fortunate with the HD820 fit so really content with their performance and getting immersed in the music but they are not to everyone's liking so really a try before you buy.....but the HD660S no such problem.
Funny how that happens...