I have an Asus M3N78-VM motherboard with GeForce 8200 chipset. Windows XP SP3 is installed.
I managed to talk to a Level 2 technician at Asus Support and with his help I was able to enable audio through the HDMI output.
The first thing I have to point out is that my computer is usually connected to a regular LCD monitor through the DVI output. I also have a HDMI cable going from the computer to the TV set, but I generally leave it unplugged at the TV end. When I want to watch a movie from the computer on the TV set, I do the following:
--- set the computer resolution to 1280 x 720
--- turn the computer off
--- plug the HDMI at the TV end (it is always plugged-in at the computer end)
--- turn the TV on and select the proper HDMI input
--- restart the computer
Upon restart, the computer detects the TV and the picture appears on the TV. There is no picture on the computer monitor, because the GeForce 8200 chipset has only single-link DVI. It can't drive the DVI and HDMI output at the same time.
I can then launch the movie after selecting it with the mouse. When the movie is over, I disconnect the HDMI cable and restart the computer. The picture then reappears on the LCD monitor. I revert to my normal desktop resolution.
The problem was that there was no audio coming through the HDMI cable. I had fiddled endlessly with drivers and configurations to no avail.
What the Asus technician told me is that the HDMI cable has to be the only active audio/video connection during audio driver installation. So he had me do the following:
--- uninstall the Nvidia and VIA audio drivers
--- unplug the analog audio cable
--- (as above) select 1280 x 720 resolution, turn the computer off, plug the HDMI cable at both ends, turn the TV on and select the proper HDMI input
--- restart the computer
Then, with HDMI active, install the NVidia HD Audio driver, restart and install the VIA HD Audio driver.
At that point, there is still no audio through HDMI. To enable it, I must go into Control Panel / Sounds, select the Audio tab and from the pull-down window chose "NVidia HD Audio". Please note that when I am not using the HDMI/TV, but the DVI/LCD monitor, this option is not available.
So, to my regular routine to get a movie playing on the TV screen, I must add the previous step before launching the movie. And...Yes! audio now works through the HDMI cable.
A couple more observations:
--- After installing the NVidia HD Audio driver, but before installing the VIA HD Audio driver, HDMI audio works automatically. The installation of the VIA driver disables it. That's why it's necessary to go into Control Panel to select the NVidia HD Audio driver when using the HDMI connection
--- The VIA HDeck configuration panel is confusing regarding SPDIF and HDMI. You have to click on the little green triangle for unseen options As I'm not using a SPDIF cable, I have disabled SPDIF and HDMI in the VIA configuration panel. I understand the SPDIF pane in the VIA configuration panel is used to send (or not) the HDMI signal into the SPDIF cable. I will have to experiment with this when I get a discrete video card and connect a SPDIF cable from the motherboard to the videocard to send audio through the card's HDMI output.
--- People who have the motherboard connected only to a TV set (no DVI / monitor) through HDMI are most likely having no problem, as all their driver setup has already been made while an active HDMI connection was present. That might explain why there are people who report no problem with HDMI audio. The problem arises when one has installed audio drivers while only the DVI video and analog audio connection were in use. Any attempt to subsequently get audio through HDMI is doomed.
That's it. I hope it helps.