I like to hear the game sounds just through my speakers and just voice chat through my headset.
I use the onboard sound of my motherboard for the speakers and I bought a dirt cheap £10 pci soundcard to plug my headset into, that way I can separate the sounds exactly as I want to.
The same would work for you, you could use the hdmi from the graphics for sound to the tv then add a cheap soundcard for your headset, that's assuming you just want to use the headset to chat.
If you use programs such as xfire/skype etc then you can set the input/output devices accordingly.
Cheers
Paul.