a couple of things to note...
A: nobody can help you with out you first giving them some info on your car
for instance, you should always tell people what the exact year, and engine. example 03 3.9...
in this case you will also want to tell everybody which radio option you have.
the options include:
base (radio and four speakers) with one speaker in each door
premium (radio and 12 speakers and two amps) two speakers in each door (still looks the same from the outside) two subs with an amp and two center console speakers
THX (nav radio and 10 speakers and two amps) two speakers in each door, two subs with an amp in the rear deck, and a 4ch amp in the trunk.
B: this has been covered many many times, search around and you will find your available options.