wierd idea

Does anyone know of a way thatI could hook up a mixer in with a car stereo system. I'm thinking it might be kinda cool is I were able to have a few 1/4" mono jacks so that me and a couple friends can hook up our guitars into the car's sound. I currently am just planning the sound system, so I am still flexible in how stuff is done. The only thing I am sure of at this point is that Iam going to use two 15" Rockford Fosgate Punch subs, and I want to seperate amps. One for the subs and one for the rest of the system. I would like to use RF amps, and I have never heard one of their amps sound bad. I am still open to suggestions. TIA!