I had the HE560 for about a month. To me it's a lot closer to the sound of the HD800 with a prominent, detailed treble and very tight bass that has extension but not much weight. The real deal breaker for me was comfort. I found it almost painful after a short amount of time. Sennheiser really has the comfort issue solved, at least for my head shape (maybe because I'm mostly German).
for me, an HP that is "complementary" is one that has a markedly different sound profile, not the same, as another HP (e.g. 650). I find the clarity, imaging, tight bass, speed, and treble texture (among other traits) of my 560 to be distinct from the 650 (which is stlll a great HP for my music).
I like my complementary headphone to be a different sound signature also....leaning toward the RS1 at this point....always was a big fan of this can for rock music.