TV sound through to computer then to 5.1 system?

It should be possible assuming you have both an Input and Output spot on your sound card. Sadly I've never experimented with doing this so I can't verify it works. Personally, I just port everything through my receiver. Computer included. Any particular reason why you want to set it up this way? :)

Ahh ok. Well, I really don't see why you couldn't. There is a line in port on most audio cards. Don't know what kind of quality you'll get though, depends on the audio card :)

The green port is out and the blue port is input if I remember correctly. You'll most likely also need to grab yourself a wire with RCA on one end, and the small headphone type jack on the other end.