I think Alpine are probably one of the better head units to go for, also the more expensive Blaupunkt range are also pretty good, a good indicator as to the quality of the head unit is see if it has a decent pre out section and at a voltage of 2 to 4V, this means that someone has actually given at least some thought to these units being used in a quality set up. Forget the meaningless wattage claims, these are pure marketing bull that was started by the japs and would quote ridiculous peak outputs of 100's of watts.
Speakers are a bit of a mine field but I have mentioned some makes before like Infinity, Focal, JBL, Dynaudio are usually far better quality and produce better sound than the Pioneers, Sonys etc who simply dont put the technical effort into making their products like a dedicated speaker company does. If you can run new independant wiring to the speakers this will improve the quality, dont need to go mad here but a decent ofc (oxygen free copper) multistrand would be fine and if you are running a seperate amp use a screened signal cable.
Dont get too caught up in the power rating of the speakers, most of the aftermarket stuff will cope very well with the normal headunit, the efficiency of the speaker will determine how loud it will actually go, lower efficiency speakers driven by large power amps in my experience always deliver a cleaner more controlled sound, the placing of the tweeters is also very important, the tops of the doors is a compromise but OK, if you can get it higher at about ear level via a pillar mounted unit you will find the stereo imagery improved quite a bit, a rule of thumb in domestic hi fi is the tweeter should be at about ear level when you are sitting in front of the speakers, bass is not directional and that is why bass unit can be placed more or less anywhere.
Just a comment on Mitch who says sound is subjective, audio is like anything you never know what you are missing until you experience something better, we all love are Alfas but if we jumped into a Bugatti Veyron would you not think we were missing something before.
Thats not to say just because its expensive its good, far from it, ive heard hi fi costing tens of thousands sounding bloody awful and a little system put together for a few hundred sounding amazing, in audio its all about matching the components and just following a few basic rules about speaker placement and using some good cabling to hook it all together.
Last edited by jossbay; 18-09-12 at 23:36.