I'm not sure what would be damaged by applying the wrong voltage to the motherboard, but maybe the fuse stopped most of the damage.
Out of those 5 wires, find out which ones are a common ground, and which ones carry the +9v onto the main board and where they go. Start at those points and work your way in.
The little fuse board doesn't appear to have much on it. The native 9v might be for running the drive and possibly the screen. I would think it gets converted down to 5v or 3v somewhere on the main board to run the logic and processors. Find and trouble-shoot that section.
Be on the look-out for a schematic for this model or similar Audiovox model. You can also lookup DataSheets for the IC chips you can identify. See what they need as far a running voltage and test those pins. If voltage is absent, work your way back.