The optical output on a tv is for getting 5.1 surround from the built-in tuner, from local HD channels, while using an antenna. It won't piggy back 5.1 surround from other stuff. If it will even pass audio that way at all, it will downmix it to 2.0 (stereo), so the best you'll get is Dolby Pro Logic (simulated surround).

You'll need an A/V Dolby Digital receiver, to do what you're talking about. You can setup a computer as a home theater also, which may be the best way for you, since your speakers are computer speakers...