I have installed the focal k2 component set in front and uprated rears to coaxial 4".
Instal link i did here..
http://f10.5post.com/forums/showthread.php?t=1213339
I did not have the funds to do full upgrade straight away so i choose the focals imo pretty much as good as anything out there, vast improvement over stock (not amplifed yet), rears were not a massive concern to me, i fitted a set of in phase coaxial 4", marginally better than stock.
Oem subs are dog poo! So they are next on my list just saving at present and weighing up which ones to get.
Finally it will be an amp and one of technics harness' to finish it off.
Good luck with your install, and just go for it and get stuck in
