I added 2 rear speakers (GB neo8) spliced of the stock amp and mounted in the middle between the seats. I built a shallow speaker box 13" H x13"x W x 1-1/4" D. I didn't get all the performance I expected but I can now hear the music coming from the rear

 

Very clever solution.

 

if anyone is interested in adding rear speakers you can splice into the speaker output wires at the amplifier, run the wiring under the sill plate and carpeting coming up behind the back of the console. I got the speakers half off at parts express
Bohlender Graebener neo8 s planar transducer 4" w x 8" h x .5" d very thin . Used the attachment holes for the spring loaded clips so you can always return it to the original stock look with no damage.