I have grafic card nVidia 9800GT (width HDMI output)
motherboard: Gigabyte GA-EP43-S3L
I want to connect over HDMI cable PC to TV.
On motherboard is SPDIF out on board, if I connet it to my grafic card over 2-pin cable, what quality of sound have I then over HDMI, is it only stereo or i.e. 5.1 channel sound quality? Manage motherboard send 5.1 channel sound to grafic card and can grafic card accept it? and send over HDMI?
The first one I built has an abit IP35 Pro Motherboard that has SPDIF sound that connects to the video card (an MSI 8500GT w/ 256MB) I had this connected via HDMI (only) to my receiver and 5.1 surround system.
Sound quality was very good, but improved greatly (to excellent) when I stopped using the on-board sound and installed an HT Omega Striker sound card (this card had no on-board SPDIF out header, so I made a cable to connect the video card to the coax SPDIF connector on the rear panel, some video cards come with this cable).
That PC is now in the basement running on a 2.1 PA system through analog out, with HDMI going to the Plasma display (sound & video).
My newer Upstairs media PC has an abit IP35 Pro xe and a MSI 9400GT with 256MB, with an HT Omega Claro 7.1 (only using 5.1) it's connected via HDMI (only) to the same 5.1 system the other one started out on. It sounds fantastic.
It's too late to make a long story short, but the SPDIF-to video card HDMI-to sound system is a good way to move the 5.1 sound from your PC to you sound system, so good that improving your sound card will be a great upgrade.
If you are just connecting the HDMI cable to a TV, you will only get stereo, since your TV likely has only 2 speakers.
If you take the digital audio (via optical or coax SPDIF) from the TV to your sound system, you will only get stereo no matter what goes into the TV (all TVs I know of only supply 2 (stereo) channels out their digital connectors).
So ideally you would connect the HDMI from your PC to your receiver, then HDMI from your receiver to your TV (to get all the multi-channel goodness).
P.S. Both PCs have an LG Blu-Ray/HD-DVD player, and movies sound fantastic too.