In all the cars Ive owned Ive always installed massive audiophile grade equipment in my cars. But with my MR2 (AW11) I decided there is no need. The MR2 is a sports car and I think all it needs in terms of audio is a decent head unit and 3-1/2" Speakers in the dash. Thats it, No subs, no amps, no components.
In my car, my engine and exhaust is so loud it blocks out alot of the sound. And dont even think of putting a subwoofer in the trunk you wont hear it. I had a 8" Bazooka Tube behind the passenger seat and that sounded great.
lol well which model car do you have? again, at mr2oc, there is a complete write up and pictures of someone doing a 10" in a mkII but anythings possible.
the best defense against exhaust noise is sound deadener. A company called secondskinaudio.com (iirc) get the damplifier or d.pro. either is the best stuff in the industry(better than dynamat cheaper too) after blocking road noise and exhaust and whatnot, your car will be a less stressful, more comfortable ride. and much better acoustically as well.
the best set-up would be a decent component set up front, and an appropriate sized sub for the type of music you listen to. the rear speakers are just fill, and in a car as small as the mr2, there is no need if you have good front speakers.
few things to remember:
1. Just about all decks under 500 bucks are the same for decoding/playing music. the difference is quality of parts, features, and power of internal amp etc.
2. the power ratings on HU are usually max, not rms. so figure about half what it says. for example, the sony 52x4 is about 17 watts per channel so be ware.
3. ifs your going with a component+sub setup, look into a 4-channel amp. this will power your two components and bridge the second set of channels for the sub. so find a HU with 4-5volt pre-amp output for best quality.
4. the best audio mod is sound deadener. it can be small patches in the right spots adding just a few pounds, or doing the entire car adding around 50lbs. though if your worried about lots of sound stuff, your prolly not concerned with 25-50 more pounds in the car.