2002 Sound System

I own an '02 Merc Mountaineer with the basic single CD/cassette sound system. It has 4 speakers - one in each door.
I would like to add speakers to it with an upgrade to the receiver. I'm thinking that the car might already be wired for more speakers.

Can anyone tell me if there are additional speakers with the premium systems and where they are located?

Thanks,
Steve

P.S. This basic sound system is weak...as in reception and bass/treble quality.

I've redone the speakers in my 02 Explorer. I found no evidence of additional wiring. However, just changing to high end speakers made a big difference in sound. You'd be hard pressed to find an aftermarket system with a more sensitive reciever than the Ford. I drive in mountainous areas and the Ford system pulls in FM stereo where many of my other systems (including JVC, Kenwood, Clarion, phillips, sony, etc) have failed. I've also found the Ford systems to be incredibly durable, while I've had about 50% failure on my aftermarket systems.

Could someone tell me how to take the panel’s front and back off on a 4 door Explorer, so that I may insert some new 6x8’s? I have a panel tool to remove the panel, but I am finding it rather difficult to pinpoint where the screws are and the panel pins. Does anyone have a picture of the inside of one of the door panels for reference? I am doing a major overhall as far as a system is concerned...LOL In-dash dvd lcd cd tuner receiver, 3 amps, crossovers, 1F CAPS, Hopefully an OHIO Generator alternator pushing about 180AMPS (Have to find one) new Pioneer 6x8's, and one sub.

Thanks for any and all info,

bstaggs