I am having issues getting 5.1 Audio, the only option shows as stereo in Windows 7 64bit

I have the HTPC connected by through the GT440 > HDMI > HDMI Splitter > 2 Flat Panel TV's in separate rooms and to Denon Amp > HDMI to LG 3D TV 

Computer is made up of the following
AMD Phenom II X4 840 Hynix 4GB DDR3-1333 ASRock 890GM Pro3 Asus GT 440 1GB Samsung SH-B123A Blu Ray AVerMedia AVerTV TwinStar Silverstone LC17 Case

Denon AVR 391 Amp (set to Amp)

PC Audio Option shows Nvidia HD Audio Denon Amp but only shows "Stereo" listed

Amp works fine with MySky through another HDMI splitter connected the same sort of way.

Any tips or better way of setting this up?