You need an amplifier. There's no way to connect your car's speakers directly the computer.
i've been looking into the carputer and getting stuck on how to hook up the speakers to it. I would be replacing the head unit with the monitor and looking to run centrafuse. i would like to keep control of balance and fade if possible. any suggestions? on top of that here is how my oem system is hooked up:
Hi Chris. You don't really want to start doing that. As kegobeer suggested an amp would be the best solution. However you could probly use an FM Modulator or one of those tapes (not sure what they called) to connect your pc up to your existing head unit. Would probably be the quickest and cheapest way, but not the best.