On the rear speakers--check the wiring diagram very carefully. If it's like the '99, the rear door speakers are wired parallel with the respective rear deck speakers, and all are 8-ohm, rather than the standard aftermarket 4-ohm. You can disconnect the door speakers and then switch the rear deck speakers for a good set of 4-ohm 8", but you might run into problems if you switched the rear deck speakers to 4-ohm and left the rear doors in the circuit.
Do read Jim Rothe's explanations, even if you don't want to get into the expensive Dynaudio setup. Piece of cake replacing the rear deck speakers, even if the holes don't line up. However, if you have plenty of oomph in your rear channels and like the factory speakers, you can leave them in without the rear doors--the 8-ohm circuit will take a bit to push, but no danger of frying anything. Door speakers are kind of kinky due to factory-specific mounts. Just pull the door panels and unclip the connectors and tape down the ends. Have fun, and post the results.
--
We have met the enemy and they is us. Pogo '99 S70 cop car : T Roosevelt Rough Rider tires& suspension, Walmart fog/driving lights, speakers by ebay, 2 old Volvo amps cranking out 8x20 W, ambiance by Pall Mall, trim by Le Duc d'Tape