As promised... this is a guide on how to get sound working on HDMI connection from the 8800GT/9800GT/9800GTX to LCD tv. Many people say that this feature is not supported, and as yet there is a lot of misleading info online. So even if you have one of the many graphics cards that have this feature you may not even know it's there.
First having had a good look around, there seems to be a discrepancy on which cards have this feature or not. I have noticed that most, if not all, non-reference 8800GT/9800GT boards HAVE IT and all 9800GTX's. If you are not sure whether your card has it or not just look next to the SLI Link on your board or in the case of the 9800GTX it should be between the SLI Link and the 6 pin power connectors. Here are a few examples:
Next: Q:I have that connector but no extra cables came with my card?
It's easy... I used some redundant case headers. The type that you use to connect case LED's or USB ports to your motherboard.
Cut 4 of these as long as possbile, then join 2 sets of 2 together at the middle and insulate them with tape, and now you have connectors.
If you are using onboard sound go to step 2. Otherwise step 3 for Creative labs cards with an SPDIF IO connection on the card.
2. Onboard Souncards:
Now you need to dig up your motherboard manual or download it from the manufacturers website. You are looking for the page that gives you information about the SPDIF "OUT" on your motherboard (assuming you are using onboard audio). I have used my motherboard as an example. you need to look at the specifics of the one you are using.
Now that you know what to look for... Find it and connect only the SPDIF_O Jumper. For the time being.
SKIP TO STEP 4.
3. CREATIVE LABS CARDS WITH SPDIF-IO CONNECTION INSTRUCTIONS
Find the header labeled: SPDIF I/O (I have used Soundblaster Audigy as an Example)
(Thanks DEC_42 for the pic) Assuming your Creative card is in a tower and upside down it will have a row of 5 pins on top and a bottom row of 3/4 pins depending on which model Creative you have. Connect the header to the first two pins on the left top row. (Shown in red box the DIAGRAM)
Now assuming you were to use the wires on that motherboard header in the same orientation... Green on the left and white on the right you need to disconnect the white one at the point where you joined it to the other header that goes to the graphics card. That is the ground! Once you establish which pin is the sound then you connect that white one back up.
Connect the SPDIF OUT from your source (soundcard/onboard sound) to either of these pins (On the graphics card) and test in windows
(MAKE SURE YOU DO STEP 5 OTHERWISE YOU WILL GET NO SOUND)
Test both till you get sound, then connect the SPDIF GRND to the other pin.
Don't forget to shut down before messing with stuff inside your case. I will not be held responsible for your new hairstyle.)
Now power up your system and go into your sound control and find the checkbox to enable digital I/O and enable it.
Hope that helped a few more of you.
Voila you have audio over HDMI.