I'm still undecided if I want to buy 560S. I have the 660S and I'm super happy with it, not sure if 560S would be better in any aspect. Personally I have very different opinion than most of the 660S owners. I don't think the 660S has a narrow stage. With properly mastered song (just regular songs, not talking about binaural) and with good DAP I constantly feel certain instruments are coming from my room and not from the headphone. I have the hd800S as well and yes they are wider, but I feel the HD800S achieves this with some kind of trickery going on (either by introducing dips/peaks in freq so certain elements sounds more distant, or the headphone itself adding very small nuanced artificial echo, which makes stage bigger). To me (with my particular set of ears) 660S sounds better than 800S. It is more natural, also I feel it is more resolving in upper mids and treble and has better imaging (I still like HD800S though and listen to it from time to time, it has very unique sound). 660S also don't lacking in base department. With low frequency sin sweep at 25Hz it has ok volume already which is good in my opinion.
I also don't hear the Sennheiser veil everybody is talking about. I have a couple other headphones and many IEMs almost all of them are more "veiled" than 660S.
I'm only looking at the 560S as a possible buy because I have the new toy upgrade itch
and the tuning might be better for movie watching / gaming (HD800S falling off of my head, not enough clamping force
and constantly have to readjust, 660S is best for music listening). I'm looking forward to hear more 660S vs 560S impressions going forward. Also, 560S is not available in Hungary yet