Got a Series 4 Samsung 450 plasma with PC inputs. Plugging in the audio failed w/ DVI/HDMI video. Turns out it was expecting audio from the HDMI on my video card. But there was no audio coming out or any way to select nvidia audio.
I had a Sound Blaster Audigy card already installed. I disabled it from Device Manager, rebooted, and now Nvidia audio took over as main sound device automatically. Sound is now coming out of HDMI cable into TV with streaming netflix. awesome.
btw, the motherboard builtin sound had to be disabled at the bios level first, but I did that in order to install the Audigy card a year ago.
Windows XP SP2, 64bit. The ability to switch audio devices is apparently terrible in Win XP.