Surround sound through Optical cable

Hi,

My motherboard is Gigabyte P35 DS3R and spekers are logitech Z5500.Am unable to get surround sound through optical cable.Sound comes from only the front left and front right speakers.I get 5.1 from direct coaxial cables but not optical.

I have tried different content ....DVDs,5.1 AC3 files.Tried different players Window media player,VLC,PowerDVD but am not able to get true 5.1 through OPtical out.

In the Realtek HD audio manager also when i test for the speaker setup,Sound comes from only the Front left n right speakers.I have been looking for a solution for quite some time.I have read on some forums that the optical out provides only 2 channels and not 5.1.If thats true it is pretty lame to use the optical out.

Will buying a coaxial digital (S/PDIF) out cable solve the problem.
What are my opther otions in terms of sound cards.Whats the cheapest option???

cheers

Optical connetion is digital signal that will carry compress audio up to 7.1 or 8 channels. You need to set you player like PowerDVD audio output to SPDIF, Then you need to your audio console to output SPDIF and not speakers. However Realtek can output digital and anlog at the same time but make sure you sellected spdif digital.