this may be a dumb question but i'm kinda new to all this. if i just wanted to hook up 1 sub and 1 sub amp to my car would i need to put in a new HU or anything else?
you dont have to have a preamp out, you can get a line output converter, basically it converts your high levels to your speakers into a line level your amp can accept. some amps even have these internally. It is not the best choice for sound quality, but it will suffice. If you just want to do a simple, budget system, this is fine. They're pretty simple to install as well.