Im getting the Onyo HTS790B system and the subwoofer doesn't have enough 'juice' for me. What conection am I looking for to connect a 2nd woofer? And the Sub that comes with the system is not magnetically shielded so does that mean im going to have to place it the back? I dont really have any space on the sides because the TV (Hitachi 50'' 50v720)Is on the corner of the room.