The 4 speakers I fitted were all 6.5 inch. 2 Component in the front and 2 composite in the rear. My Pioneer unit can switch between the rear channel just being sub or sub+rear and I tried it, the difference is quite noticable. With all 4 speakers + sub the whole car is filled with sound, really crisp and big if that makes sense. So if you can afford it I would change all 4 speakers, just look at where the rear ones are sited, right behind your ears!!!!