It all depends what kind of money you want to spend really. I am not sure about your specific car, but its easiest to hook up amps to a deck that has rca preouts. So I would definitely get an aftermarket amp because no stock cd player I know of has them. Then go with a small 4 channel amp like CX said, size depends on what speakers you get. Get 4 good quality 2 or 3-way speakers(size depends what will fit/what you want). Hook the 4 channel amp up to those. Then I would get a good single 12" sub and put it in a badpass box and get a single channel amp to push it.