I use the external speaker jack that jerry is talking about and run an audio cable to the aux in on my pioneer head unit and then its over my jeep speakers like your asking. Down side is obviously can't leave it like that and listen to the radio so only usefull on the trail.
The Budget Brawler. AKA Berta
97 sport 4.0 5 spd
6" RC Long arm 35" MTRs
HP30/D44-locked 3.55s (4.56 "soon")
KC/Hella, Engo 12k, Home made Hand throttle,Home made On Board Air, Etc etc.