I know this post is old, but I figured anybody who has a 2nd gen and doesn't know how to do this will get a little help.
Currently, I have polk db series 4" in my dash and polk db 6x9's in the cargo.
Also have a Pioneer AVH-P3100DVD in the big Double Din opening.
In order to get to the speakers up front, you'll have to remove about 8 screws from the dash and 2 10mm bolts.
The drivers side will not come off all the way, you'll just have to pull it down. Also, remove the small ignition panel.
The passenger side, the screws are mostly behind the glove box and you'll have to disconnect the wiring to the stock speaker box with the 4" speaker and the glove box lighting.
Once you have that done, you can basically just plug and play 4" speakers, although not all will fit, I have mine held in with 2 screws each and surrounded with some foam tape you can get from anywhere.
The back speakers are not as easy.
You have to lower the tailgate, unscrew the lower panel where the trunk meets the tailgate. Next, start to pop off the back panels carefully. Actually, before that you need to look up and pull off the dome light panel. THEN start disconnecting the back panels. Lower the seats, and unscrew the large bolts holding on the seat belts. Once you have all that done, you should see the factory speaker boxes. The best idea is just to remove these because the "5 1/4" speaker opening is not actually 5 1/4". I removed the speaker boxes with a lot of torque and broke two of the bolts in half in the process and then cut holes in my rear panels to install 6x9s.
Now, for the reciever.
Do this when you have the dash off.
Remove the temperature controls and the small panel right in front of your shifter.
You should be able to undo about 6 screws in either side and then be able to just pull it right out.
Hope this helps.
PM me if you need anymore info.