Okay, I'm not sure exactly what you're saying. Your speakers are (probably) driven by an amplifier in the radio. You can't just hook up a computer sound output to the speaker wires; the output is too low. Plus, when the radio plays something the power would most likely turn your motherboard into a smoking wreck. If your radio doesn't have line-in jacks on it anywhere, you need an amplifier and/or some device to switch the speakers between the two input sets.