All computers have an analog output. It's the green hole on a PC with a little headphone symbbol. You just need a cable that has a stereo 1/8 inch plug one end and RCA plugs on the other. Plug the 1/8 to the computer audio out and the RCAs to the preamp.Get the cable at Radio Shack, Best Buy, etc.
Not the ultimate in sound quality but the only conditions you stated were simple and cheap and this is the simplest and the cheapest.
Not the ultimate in sound quality but the only conditions you stated were simple and cheap and this is the simplest and the cheapest.