ATI 5750 and Geforce 7100 MoB: no audio, tried everything

Hello,

I have an Nvidia geforce 7100 chipset. To optimize gaming, I upgraded the stock 200w power supply to 750w (overkill but you never know when you need more juice), and installed a Diamond multimedia ATI Radeon HD 5750.

The graphics are great, but now when I mouse over the red X audio icon on the lower right of the screen, it reads "no audio output device installed", and I get no sound even though I've tried all the typical solutions. The audio works fine with headphones and speakers without the ATI card installed and using the original drivers.


I have done the following:

• Changed the bios settings, updated drivers, but did not flash bios
• Uninstalled the old drivers, installed the new drivers for video card
• Tried updating old drivers and new drivers, tested both, neither work with the new card (when I take out the card, the audio works fine)
• Checked for loose cables or connections, and manually reinstalled the card to rule out a connection errors
• Restored drivers and updated again

At this point I think the Nvidia MoB may either:

(1) not be compatible with the ATI card (this chipset was not built for gaming),
(2) or that the graphics card is defective.

If the card is defective can I test that myself or do I have to go through the hassle of sending it to the manufacturer? The device manager reads normally, and everything else seems to be working fine.

I'm considering installing a new Nvidia card as I am led to believe Nvidia cards work with all Nvidia chipsets. Before that, I would like to see if anything can be done for the ATI card, which I’m otherwise happy with.

Should I try HDMI audio codecs, bus drivers, etc? Do I now need to route audio through a new connector from the hdmi port on the graphics card to my stereo receiver/speakers? Do I need to flash the BIOS? Do I need a new MoB altogether to support better graphics?

If it turns out that this MoB is incompatible with this card for some reason, will a Geforce 9800 GX2 or similar work? I find no resource on Nvidia's site that discusses what MoBs are compatible with what graphics cards.

My gratitude to the hive mind if anyone can shed some light on this quandary.