I'm not 100 percent sure on the size of the rear speakers, but since you have decided to go a different route I guess it doesn't matter. If you still need to know just take off the door panels and check. If you need help with this let me know. Also, dynamat isn't going to fix a lot of the rattles that you'll encounter. If you are irritated easily by rattles, like I am, then you are going to have to take a lot of panels off and work on things like the clips that hold the panel to whatever it mounts to. Subaru uses some good clips that don't seem to break, but they can get noisy. I took off all of the clips and put a layer of black silicone on where the clip and panel meet. This will help a lot. There are a lot of cheap and simple (not always easy, but simple) things that you can do that will help your car sound better. Good luck! I recommend to amps, it'll probably give you more flexibility, especially if you decide to make any changes to your system down the road.