Based on your steps, I recommend you updating the bios to the latest one we currently have. You can get at the following link:
Besides the step above, you can also try updating the graphics card by installing a firmware.
It doesn't add up.
I would have told you to make sure through the sound CPL to show disabled devices. However, since you did a fresh install of Windows & all the proper drivers would you please try this:
Do you know how to use the PSR "Problem Steps Recorder" in Windows?
If yes please record it & upload the ZIP file.
First, I would like to say that I know this is a very old post and that I should let it die, however, after breaking my head for several hours I thought it would be interesting to share the solution to this problem.
This is due to the fact that your BIOS version is very updated. Allow me to explain.
If you look at the Bios Release Notes of your motherboard, you will notice that in the version 0016 the devs have implemented the following fix:
BIOS Version 0016 - WVG4110H.86A.0016.2011.0414.1502 - "Fixed issue where PCI graphics card causes board not to boot."
It happens that they messed up something and generated a conflict with the Nvidia video cards. Personally, I had problems with the 8400GS and the 550TI.
Long story short, if you downgrade your BIOS to the version 0015, the HDMI Audio will work correctly.
It is likely that you have already solved this problem or simply changed the motherboard (since it's been 3 years), but I think this answer can help you to give a proper end to this story.