Your motherboard has the audio codec.
You may have found something. I don't have one of these cards and I have not tried this before. If you are up for an experiment, try this:
1. Back up your system. Ideally, you have a separate partition to run this experiment. You must remove all Voodoo audio kexts, including the pre-pane.
2. Determine Nvidia HDMI audio device ID. (this is different than the Nvidia codec device ID). It will look something like this in Windows: 10DE 000x, where x is a hex value (1 through f); or Mac: 0x 00 de 10.
The easiest technique to use is Windows/Sound/Nvidia/Properties/Device_ids. In Mac, it may show up in bdmesg, lspci or ioreg.
3. Run MultiBeast; select AppleHDA rollback. If your onboard codec is available in MultiBeast, install that as well.
4. Make a copy of AppleHDA from S/L/E on your desktop. Verify that AppleHDA is v1.7.9.
5. Run Hexedit; in AppleHDA binary, find 07 00 de 10 and replace with 0x 00 de 10 four times, "x" being the value you found is step 2. No edit is needed on AppleHDAController binary.
viewtopic.php?f=162&t=22032
6. Install the edited AppleHDA in SLE, repair permissions and reboot.
7. Check System Preferences/Sound/Output for HDMI audio.
We'll try this without the DSDT HDMI audio edits. If it doesn't work, we can add the HDMI edits.
Good luck.
An apology in advance. Some of the information above may not be 100% correct as I am traveling and don't have access to my usual resources.