I've done several car audio installs, some pretty high end. For good sound quality without ear-bleed spls, I'd get the following...
- Good Head Unit, I'd like to try out an Alpine with IMPRINT, or Nakamichi for a no-frills unit with good sq.
http://www.alpine-usa.com/US-en/products/product.php?model=CDA-9887-Good Amplifier for 2 speakers + a subwoofer.
-10" Subwoofer in a small sealed enclosure. I have a smaller car, so I may put an 8" Sub under a front seat.
-Component speakers in the front door, according to personal taste. I like Focal, but they are pricey. Good installation of speakers and soundproofing in front doors is critical.
-Try using no rear speakers.
-Soundproofing. As much as possible, but do the front doors thoroughly, at a minimum. Elemental Designs makes some good soundproofing that is less expensive than dynamat
http://www.edesignaudio.com/ . I used one of Elemental Designs 12" o-series subs in a Suburban with good results before, it was a very clean sub. I haven't heard their component speakers. I completely covered all the interior panels of one of my cars in dynamat and there was a dramatic reduction in road noise. Well worth it if you have a louder car. This is moderately expensive and very time consuming, but well worth it if you think you're going to keep the car a long time.
- You'll need to high pass the component speakers (around 90 Hz or so), so buy an amp that has a built in x-over. The Sub should have a 24 dB octave low pass x-over.
- Stick with 4 ohm speakers and sub even if the amp can handle lower impedence.