I need to upgrade my sound system. I intend to add sub and amp with tweeters to the factory fitted head unit of my car. The system on now is that of Botch or Bose/Audi chrous/concert/symphony radio.The system plays well but I just need to step it up more. I like the head unit on the dashboard and would not like to change it. I've check the head unit but realized it doesn't have preouts for amps and sub, Please does anyone know what to do to add this other extras to my system.