Ohhhhhhhhh man... Those rear speakers are a *****. You need to remove the rear seat bottom first. This is easy, and will definitely help. I would then recommend removing the rear side panels. Be careful pulling them off, because the little clips seem to come apart easily (you can put them back together though). Now you can lift out the rear speaker panel.

It is possible to remove the rear speaker panel without taking off the side panels, but damage to the side panels is almost inevitable.

As for taking out the speakers, you definitely need a 90-degree screwdriver. Even a stubby is too tall, bud.

Enjoy.