I can't speak to the HD800 or HE560 but I have the HD6XX and HE400i and it powers them just fine. The volume level is getting up there but no clipping. I am also running both of those in balanced mode...love the signature from this.
Thanks for the reply. The HE400i and especially the HD650 are warmer sounding than the HD800S and even more so the HE560 so I think they will need a different signature from the source(s) to sound their best. As an example I tend to enjoy the HD650 the most (although I'm really not that found of them) from a very neutral sounding source while I prefer a warmer source or tubes somewhere in the path with the HD800S and HE560.