The electrical plug in the back will almost certainly NOT be compatible. You'll be lucky if the plug even fits, it probably won't. And even if it does, it will almost certainly have a different wire configuration, making it unusable.
The aftermarket head unit will likely come with a wiring harness that fits into the plug in the back of the kenwood unit. The other side of the harness will just be stripped wires. You'll need to buy another harness specific to your car audio system that will connect to the plug coming out of your car. Then you will have to crimp the wires of your kenwood harness to the wires of your aftermarket audi-compatible harness.
Kenwood Head Unit <-- kenwood harness plug -- kenwood harness wires >CRIMP< audi aftermarket harness wires -- audi aftermarket harness plug <-- Audi OEM head unit plug.