What head unit are you running at the moment? If you looking at high powered speakers you might need an AMP to go with it
BTW... I have a Sony "Inline" amp, I will dig it out and if you want it its yours... or if you want a West Coast Customs AMP I also have one of them laying around... lol
The inline amp connects to the back of the radio in place of the ISO adaptor, then the car ISO adaptor plugs into the inline amp... all speakers are them amp'd with minimal fuss
(Even is small enough to slip behind the centre console!)
The west coast customs amp is more complicated as it needs to be wired in
Suppose it depends what you are looking for from the In Car Entertainment system
Also got a few subs as well if your interested