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...If lighting a reception dance floor I also would need my on-camera flash to provide fill flash in coordination with the speedlight's on their stands. ...Are there any additional pieces of equipment I will need to pick up to make this work?
Since the JrX transmitter doesn't have a pass-through hot shoe, if you want on-camera flash you would need a PX transmitter to attach to the head of one of the Speedlites, which you would then mount on the camera (or better yet, on a flash bracket, connected to the camera via an ETTL cord).
The JrX receivers are compatible with both JrX and PX transmitters.
If, however, by "on-camera flash" you mean a built-in flash, I have seen a stand-off bracket made by the Pocket Wizard folk that allow you to use the pop-up flash and a PW transmitter at the same time, but I have no experience with that.