Please help me solve my HD Audio problem on my HTPC

Here is the hardware:

ASUS P5NE SLI with 3.15GHz proc, 8GB memory, 64GB SSD boot drive
Auzentech Explosion 7.1 PCI sound card
Galaxy GeForce GT 440 with VGA, DVI and HDMI output (no audio headers on card)

Yamaha RX-A800 Receiver
Samsung 40" LCD Display
Viewsonic Pro 8200HD Projector

When running Windows XP Pro, using the Explosion's coax digital output and HDMI to the receiver, XBMC plays perfectly.

Attempted an upgrade to Windows 7 Pro 64-Bit. All drivers loaded fine. I am unable to get audio over the HDMI cable. After searching the net, it would seem the video card is capable of doing it. Here are the steps I took:

Remove the Explosion card. Enable onboard audio in Bios. Load the latest GeForce drivers for my card which includes the HD Audio driver. When running the NVidia control panel, I can clearly select HDMI under audio and I see one of two sources, depending on what destination I use, either Viewsonic 8200HD or Yamaha A800. I open the sound control panel and HD Digitial Audio is the default option, others include headphones and speakers. At this point, sound is just not transmitted to the receiver when running sound tests. I can clearly see the sound bar showing the rise and fall of sound during the test.

I connected the coax digital output to the mainboard output and to the receiver. Sound works but dropouts are so significant that it's unusable.

I disable the onboard audio and install the Explosion card. I connect the coax to the Explosion and sound works a little better but audio dropouts are still appearing about every 5-10 seconds, once again unusable.

The hardware should be more than enough to play the most intensive 1080p mkv files, and in fact under Windows XP, they all play and sound fine.

What am i not doing here to make this work? Can anyone confirm that the Galaxy GT440 with the yellow fan will carry HD audio over the HDMI port? Is there a setting somewhere that I'm missing?

Should I just throw in the towel and install Windows XP 64-Bit and call it a day?

No luck there. I powered off all components. Powered on the receiver and display. Set the input on the receiver and then powered on the PC. Still no sound.

Amp is on under the Receiver setup. At this point I have to assume that the 440 will not pass audio via HDMI. I have narrowed the dropout problem to XBMC. Not sure why it's not working correctly, all the settings look good. I can run a move in VLC with no audio dropouts. XBMC refuses to play without dropouts and I've tested all the settings. Any other suggestions?

I uninstalled all drivers and loaded just the Nvidia drivers for my card including HD Audio. Same results.

I swapped HDMI cables between the PC and Receiver. Same results.

I swapped HDMI ports on the Receiver to a known working good port that will play audio over HDMI. Tested good.

So I'm guessing there is an HDMI input port based setting on the Yamaha that needs adjustment. Downloading the manual now. If anyone can point me to a quick fix, I'd be set.

I have quite a few Yamaha receivers of different flavors and I seem to recall on some you can hardcode a specific audio source to a video source. Maybe I did this awhile back and I just don't recall doing it.

For those who might like to know, I was able to get this working. On the not very intuitive Aventage receivers, you have to select the input, in this case HDMI 3. You have just a few seconds to press the up or down arrow which brings up yet another menu where you can select the audio in source to go with the video source that is selected, again, HDMI 3. Even the manual didn't clearly explain this in detail.

I had been running the Explosion card using coax out in conjunction with another video card for a couple of years. I made this change and forgot all about it. Just took a little research after adding a new video card.

Thanks to all those who posted and pointed me in the right direction.