Re: Computer to TV, sound & video on both different channels
This is a longshot but try connecting the HDMI cable to the other socket (HDMI 2) and see if that makes a difference. Otherwise I think you may be out of luck.
The TV has a PC VGA input though and you could use that by getting a DVI to VGA connector (if your GFX card doesn't have a VGA output already) and there should be a dedicated sound input for that channel as well.
Lastly, you could take out your 9800GTX and sell it on ebay and buy another 9800GTX that has a HDMI output. You would then just need to connect the sound card on your PC to the graphics card and it will output the sound through the HDMI socket. This is a kinda long-winded fix for a small problem but if you think about it you could probably break even or it may cost you £10-15 max. Its just an idea you can think about if you can't find any other good solutions.