this maybe of help gaining access to the rear speakers.
You will need to do this for both the drivers and passenger sides. First pop off the door sill.
Then peel back the rubber lining and pop off the quarter panels
Pop off just the top of the plastic panel behind the seats like you did with the front speakers.
Open up the smaller compartments on top in-between the speakers, and just pull them out (they pop right out).
On the trunk side of that same panel, lift the carpet up and remove the poppers holding it in. Then pop the whole panel out and remove it.
Unscrew and remove the speakers:
Tap into the factory speaker wire, connect the new wire to the new speaker, and re-mount using the factory screws.
Put everything back together, and you're done!