Surround Sound issues

[Squa11_Leonhart]

Optical connections are very picky with what audio format is used.

Optical connections only support pass-through of dts and ac3 formats surround sound formats. All other formats are converted to and sent to the amp as stereo LPCM.

Most games output surround sound as 5.1 LPCM which cannot be sent over optical natively (so it falls back to LPCM stereo). If your soundcard supports dolby digital live or dts connect it can compress 5.1 LPCM into ac3 or dts on the fly to preserve all surround channels for output over optical (you have to enable this option manually for most soundcards). If it doesnt support it I think you can use ffdshow to compress lpcm into ac3.

Your best bet though (if your amp and pc support it) is to use hdmi passthrough as it can bitstream a much larger selection of audio formats (including higher quality formats such as dts HD) compared to how restrictive optical connections are.
A lot of the newer AMD graphics cards have the option to passthrough audio over hdmi (i havent used nvidia in a while so cant comment on their cards).