Spdif optical output in pro logic or dolby surround sound?

Question

i've got a trust SC-5250 5.1 surrond sound card and i've connected it to my sony AV amp with an optical toslink cable. The amp supports Dolby digital DTS and Pro logic.

The surround sound works fine if i play a dvd straight from the av unit but i can't get the unit to display the prologic light when playing music or a dvd from the pc and only the left and right speakers have sound all the rest are silent.

Do i need special software (DVD or media player) to output an optical signal the amp can decode. I've tried Winamp and a couple of plugins but still can't seem to get the other speakers to work.

By the way the sound quality is so much better and the volume on the amp much higher with the optical conection. You wonldn't beliveve it till u heard it! Unreal

Answer 1

I have a sneaky feeling there is a setting for the sound card somewhere that you have to select to tell it you want to output 5.1 via optical.

Answer 2

I think the issue is with the receiver, not the computer.  Dolby Surround Prologic is really just a 2-channel format (the mono surround signal is derived from those two channels), and it looks exactly the same as PCM stereo (like from a CD) when it comes over the S/PDIF link.  You need to select the Prologic mode on the receiver as the default for 2-channel stuff.