I use a Sparkle GTX 260+:
DVI_1: 1920x1200
DVI_2 -> HDMI: 1920x1080
No problems at all, working with GraphicsEnabler=Yes.
(If the second Monitor is plugged, the card isn't in 2D-mode anymore, this means 20W more energy-consumption but has nothing to do with OSX)
Haven't tested sound via HDMI.