From what I've read, on our cars that are equipped with Bose, the amp for the speakers isn't in the head unit (which I originally thought). I read that it was somewhere in trunk, but I couldn't seem to find it.

So what exactly does this amp look like, and where in the trunk (or car) is it??

It should be in the same location as the Monsoon amp in the later Bonnevilles. If so, you'll find it mounted behind the rear seat back on the left side. There is a diagonal support it is bolted to. Access is possible by removing the trim panel in the trunk which would hide the seat back for the rear seats. It will have a cutout in the centre for the passthrough into the passenger compartment.