I have a 2010 Jag XFR 5.0 Supercharged. What can I do to get more horsepower out of it? As much as it can possibly have.

 

Change the supercharger pulleys for smaller ones so you get more air in.
Change the cats for high-flows so you get air out faster.
Remap the engine and transmission to make use of the more air in and faster air out.

You can change the air filters too but these are marginal compared to everything else.