The same holds true for the 04+ GPs, you have to remove the bottom the rear seat cushion and then you have undo the two or three bolts that secure the top portion of the back seat to the underbody, where you removed the bottom backseat cushion. Once those the bolts are removed you can take off the top portion of the back seat and then lift off the cover over the speakers and then you will have your access.
And to reassemble, just do reserve of what I said above
I hope that helps.