I experimented with speakers in my truck before I did the final install, and got great results!
First -- 4 speakers were just too many ... sound bounced all over the cab. Two speakers were best, and the best spot, for me, was in the kick panels ... but I angled each one so that the driver side speaker pointed up towards the passenger's head and vice versa.
Then I bought Sony Xplod speakers. The real trick in getting good sound is to match the wattage of the speakers correctly to your unit. The details are at my site:
Designing and Building Speaker Cabinets[/b] [b]My Radio Install
