I used to be a car audio junky back in the day. I was on a forums with soime very experienced people and they seem to recommend these brands.
CDT Audio ( have a look at their drivers) very neutral, solid mid range clarity, smooth tweeter are some comments on these. you can find them at
www.woofersetc.com.
An external amp would give you much better performance than the internal on the head unit, especially if yo go with components(seperates).
The ideal way to do it i believe is have a nice pair of component sin the front with some deadening(secondkin) in the doors to killl vibration, road noise etc. They say front stage imaging is very important as the components up front are considered the main speakers.
You can get co-axial speakers, mid range clarity might suffer, but they would be better in the bass department.
If only audio is the main goal and no price constraints a affordable set up would be:-
Get a 4 channel amp, use 2 channels for your front components and bridge two for the subwoofer(Ed, Image Dynamcis etc lot of id companies) you can later buy down the line to *** some low hz. You can run coaxials (6 x9) in the rear from the head unit.
And you know the take on JL high quality equipment at high prices. There are many quality ID companies making everything from amps, speakers to woofers in the car audio world also, if you want bang for the buck you can go this route.
Peace
satish