95 Orvis edition with no sound out of the speakers

[Torgon]

My mom-in-law owns a 95 Jeep Grand Cherokee Orvis Edition (with the infinity sound system). Unfortunately, she recently had an issue where here battery died and when they tried to jump it, the wires were crossed and it blew the motherboard for the jeep (they thought the had to get a new engine because it was spewing black smoke and having all sorts of issues). They replaced the board and everything is working fine, except the stereo system.

I happen to have a 98 Jeep Grand Cherokee Laredo, so I pulled out my amp and receiver to test and still no sound. I then plugged said parts from her jeep into mine and they work just fine. The receiver is getting power, and we checked the fuse listed for the stereo and it's fine.

What am I missing? Is there a separate fuse for the speakers not listed in the manual?