Can you just drop in rear panel replacement speakers and door replacement speakers even with the stock bose amps, or do you have to run fresh speaker wire throughout and connect direct off the headunit (assuming no aftermarket amp for regular speakers)?

 

you can just replace the speakers if you want...seems like most front speakers will need a spacer to clear the window (OE speakers aren't too deep, so aftermarket speakers will extend further into the door)

*I just clipped the OE end connector that attached the OE speakers and spliced on the connectors that came with my speakers - super easy. the hardest part was taking all the paneling apart...but there's some good threads with pics that will help you along the way.

-Peter

btw: front and rear speakers are both 6.5"

 

Good job I read your btw: cos I was just about to ask what size the fronts were. Some sites have the front of the Z as 5 1/4"