I'll be using the factory amp's location as a future mounting spot for my XM tuner module. It'd also be a great place for a remotely controlled eq/dsp module.
There are some amps out there that are small enough to fit. I'd take a look at the Infinity and Blaupunkt digital amps.
Blaupunkt PA4100 - 100x4 and 10-15/32"W x 2-5/8"H x 9-7/8"D
