DIGITAL SPDIF OUT ONLY IN STEREO!!!

I have the MSI P45 Platinum motherboard WITH A DIGITAL OUT SPDIF (optical fiber).
Connected to a Sony HT-DDW685 with the same spdif
BUT THE SOUND IS JUST STEREO!!!!!
why?? if the motherboard has 8 audio channel and the HT can receive blue ray for this entry.

anyone with any suggestions

thanks

I am using the same program that brought the motherboard.
in the normal output (plug) is set to 7.1 Channels
and the Digital SPDIF can only configure the balance (stereo????)

the program no matter, crysis, power dvd 8, etc. all in stereo.

thanks for the reply.

Spdif is usually used for either 2.0/2.1 (digital PCM), or 5.1 (Dolby Digital/DTS), or through various upmixing tecnnologies (Pro Logic/Dolby Digital Live/DTS Interactive).

Basically, unless the output program in question supports upmixing, or unless you have a reciever that does the upmixing for you, you only get 2.0 as the output.

Also note, Windows has some issues getting beyond 2.0 using Spdif, as Windows expects a 2.0 as the output. Make sure that (I'm assuming Vista here) 'Speakers' is the selected output with 5.1 selected as the speaker setup, not 'Digital Output', which assumes 2.0. (Stupid, I know).