What I did in my coupe was to remove the small access panels used to get to the tail light bulbs. I then I used them as a template to make a replacement panel out of fiberglass FRP - we have scraps at work. I made a cutout for the speakers in these panels and covered them with sticky backed black felt. I mounted the speakers in these panels and mounted them in the openings in the corners. The FRP is fairly stiff, but will bend enough to take on enough of a curve so they look factory. I just tuck the upper edge of the panel into the same place the factory panels fit and run two screws through the bottom.

I have a Blaupunkt MP66 Memphis head unit which is wired to the factory amp with an adapter plug. I'm using the rear RCA outputs to feed a small amp in the back to run the rear speakers. It makes a HUGE difference in the sound. Really fills in the soundstage. I started with a set of 3-1/2" Pioneers and recently replaced them with 5" MB Quart 2 ways. Sounds awesome - I'm sitting right in the middle of the music. If I need to replace a tail light bulb I just remove the two screws on the bottom, slide the speaker panels out and lay them in the back. Easy and fast.

Tom