nVidia MCP55 High Definition Audio

I was lucky enough recently to acquire an XFX 790i motherboard with which to build a mythtv rig. This worked well on Ubuntu 8.04 except the onboard soundcard(nVidia MCP55 High Definition Audio) doesn't seem to configure properly, it is detected as HDA however. It seems to simply run in the 2.1 audio mode and when I attempt to run some other audio sources after watching anything on mythtv; they are all muted. Is there some configuration trick I can use to make it reveal it's 7.1 glory, or is this card just lacking in linux support and I need to make other plans?