forget upgrading the rear speakers. upgrade the fronts with a quality crossover and good tweaters. silk dome if you prefer softer vocals, more life like. i ve tried a good few. next, you ll need to look at a sub box of a sort. then, 2, 2 channel amps to run the fronts and the sub. head unit will run the rears. use good quality wiring all the way. you ll not need anything more! all depends on your budget of course. but this is where to start. hope this helps some. cheers......