The reality is, there is little you can do, without spending a lot of money. Jeep has spent millions in development to get the best performance/fuel economy/emissions reductions possible and reasonable. If you want a different sounding exhaust, get a different vehicle or a different exhaust. The more you complicate/modify your vehicle, the harder it, generally, is to fix.
If you are into adventure travel or looking into it, there is a lot of good advice and help here.