I found no hardness or harshness, nor sibilance. Just a slight tizz/shimmer. And I am convinced it is a trait of the headphone. Seen in measurements too and reported by others, even a long time ago with the pre-prods.
Edit: with production pads
I heard this characteristic at times, but most certainly only brought out by the recording/mastering of the source material. I have wonderful full recordings with plenty of cymbal work that are just dead on live and natural sounding (I am a drummer so quite familiar with cymbals). However, there were a few instances where some material would exhibit this shimmer around cymbals (most noticeable with cymbal work of course). Again, that is as we know the risk and reward of revealing/detailed headphones; on occasion you aren't going to like everything you hear. Fortunately this is not a common occurrence at all, and frankly rather predictable for me - I know what material I have that is hot mastered or poor in general so if I elect to listen to it, I know what I may get and typically I turn the volume down. So yes, I would also agree there can be the "shimmer" or extra energy around the edges of the treble at times. Still, I wouldn't give up the glorious capability of the 560 to be shielded from some poor recordings, those recording are poor whatever you play them through. If I opt for a headphone that smooth's some of those edges away, it also means that on nice recordings some of what I want will also be smoothed away so I guess you pick your battle.