You're likely to experience a lot of signal loss without heavy gauge wiring. As well, you shouldn't connect anything that's going to feed back into your stereo amp.
I know that if you're trying to power speakers off your pc's sound card it won't work but I have the reverse scenario. I have a set of 2.1 computer speakers that hook in via a 3.5mm cable. I want to hook these up to existing speaker wire that's already running through my house to my stereo amplifier. Is there a way to do this or should I just give up?