I've got the HD-600's which I'm using with the GS-Xmk2, and I'm very happy with how they sound. I'm using a pure silver 4 pin XLR custom cable with the 600's, which I find does improve the SQ quite a lot.
I might eventually try the HD-800's with my GS-X, but they'd have to be on loan.
At the same time I'd also be wanting to try the TH-900 and HE-6.

























