well fitting ice in the lexus its great mines being done, removed factory h/u replaced with alpine tv screen and in dash dvd and fitting dvd 6 disc changer in it, u can uprate back speaker with some 6 x9 make it really up to u how much u want to spend???
front speakers i go for sumthing like a set of components that what i gone for but i got some custom door builds done one off jobbies they look great and the sound staging is phat,
i used to have twin 10 inch subs custom built for the lexus the port fired into the rear shelf so u would have to make a hole in the parcel but u can hear and feel the bass, im sellign them cause i decided to go 15inch sub hehe,,
putting caps across the speakers does not increase impedance it only acts liek a crossover..
amit if u wanted to change amp u might aswell change speakers, i dont think u find a decent amp to go back in that place, trust me i taken my whole interoir out in my lexus... :duh: