I am looking into putting a subwoofer into my Forester. I can either buy a new amp for my system or use my old 4 channel. If I don't buy an amp I would buy a set of components for the front doors. I would bridge the one side for the sub and use the other side for the components. I don't know much about amps. First can I use do that to a 4 ch amp? How will it sound driving a sub and a set of components? What are your thoughts? Thank you for your help!