i want to connect my PC to my Blu-ray Home Theater system, just for the sound. The only "in" connection on the blu-ray system is the optical and analog(stereo).

i want know do 5.1 audio signals(be it dts, Dolby, trueHD, etc) play through optical connection?

They do for my PS3, if the PC gives out dts signal it should but I am not sure it will?

If your PC is outputting a 5.1 signal then an optical connection should carry it. AFAIK only certain sound cards output a 5.1 signal though.

Your motherboard will need to be encoding the audio too if its not already compressed optical can only do compressed audio on 5 channels uncompressed PCM will only get you 2 chan

As long as your pc can encode the into the same type of signal that your player is able to decode, then yes. A lot of times (especially on pc sound cards) digital optical inputs on devices are only capable of accepting or decoding PCM (stereo) signals even if they are able to encode into a Dolby or DTS format. what sound card and what blu ray player are you using? usually the answer can be found in the device's manual.