It is a good match IMO, transparent, neutral but without etch or glare, very refined. When you consider the tech and capabilities nothing can get near it at the price.
Possible downside is that some might find it too dry or neutral.
Master 9 is apparently warmer, GSX mkii I heard recently was also warmer. I would like to hear the Master 9, but not sure if it needs the extra class A bias just for HD800. The better internal hook up wiring can't hurt either.
Why not? Just asking... Are you thinking Class A = overly warm? Or what are you saying here?