Do rear speakers add anything to the sound in the front? I have rainbow 8.2s and a 10inch sub up front. Whole van is sound deadened and the sound in the front is good (after quite considerable messing about!). All sounds pretty good but I still think my old car was better. I laid the speaker cables when doin the electrics so wondering if I should find a place for 2 6 inch speakers? And if so what spec?