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Few options depending upon what you are looking for from a new system.
COMPACT amp will fit under a passenger NON power seat and can be completely hidden away. When I say compact I am talking like 2" or less tall (unless you want to screw into the floor of the car) and preferably less than 14" long by 9" or possibly 10" wide. Taller, wider, or longer than that you run into concealment problems and rear seat height clearance as well as seat adjustment problems (adjustment handle sits inside the track width of about 12" or so)
Could build yourself a covered amp rack behind the seats with some small fans to help keep things cool.
Could also raise the trunk floor a few inches and build yourself a nice custom amp rack and sub box that could be totally hidden. Or just mount on the back wall like many people do with the coupe body style. Another option is to mount directly behind the rear seats like Polishdude and DPG did.
you could put the amps where i have mine but put a tinted piece of plexi over it with some fans. with some clever backlighting you could have a nice stealthy display piece