Originally Posted by Kevin108
There are kick panel mounts available as well as adding an additional factory sound bar to the ceiling.
This. Sound bar up front and in back, or kick panel front with sound bar in back. Some guys mount speakers in the tailgate, but that's more difficult and can make it hard for the gate to stay up due to the extra weight.
No matter what you do, the sound imaging/quality will suck, but XJ's suck for sound to begin with. Since you're going doorless, I doubt you care about that stuff anyway. I'd personally go with a sound bar front and back because legroom sucks the way it is without speakers sticking out of a kick panel.
Even if you don't buy from them, use Crutchfield.com to get loads of info about car audio--they have a bunch of reference material in addition to being a store. You can input your year-make-model, and they'll show you everything that fits and even make mention of things that will fit with slight modifications if it interests you. IF you order from them and have provided your vehicle info, they'll often provide installation accessories for free along with a very easily understood master sheet of instructions specifically tailored to your vehicle. Their customer service is excellent.