I replaced my back speakers, front speakers and head unit. Front speakers sound great, back sounds shitty. The rears are 6x9 Alpines and all I can get out of them is a muddy heavy bass too. Which sucks kinda, fortunately the front speakers override alot of that but it's still quite annoying.
I liked the stock system but the CD player stopped working and I blew one of the front speakers and I blew a rear speaker as well.