If you were to setup your audio system correctly then rear speakers are out of the question unless you use some specific processing techniques. Otherwise, they just mudddy the stage. My vote is to go without them. Add something up front, throw in a subwoofer (sealed facing the cabin is my preference), and call it a day. If you want ported or bandpassed then to get a good quality setup takes a lot of time testing and then you have to build a specific box for a specific driver. If you want it to go boom boom boom...just throw in a bazooka tube and call it a day They sound decent without the worry or hassle.