Early Friday morning at CanJam, I listened to balanced HD800s from HeadRoom's BUDA stack. At that point in time, I wasn't sure if I was going to keep my HD800 order or cancel it. I listened to it for about 1/2 hour while Tyll and the Sennheiser guys unpacked. I can say that a balanced HD800 and BUDA is a world-class combination. After that 1/2 hour, I knew I was going to keep my order (and did).
I haven't had the pleasure of doing the same listening with a GS-X. From every thing I've heard and read, that is also a world-class combination. In my mind, this is reverse Hobson's choice. You can't make a wrong decision.