Perhaps strange question, but does changing an AUX output to stereo turn the single XLR into a stereo XLR?
Thus needing a splitter cable to feed the stereosignal into a IEM transmitter
Although making it yourself is quite easy if you can solder, and a whole lot cheaper.
In the attached picture you see on the AR2412, line out 1 and 2 with one of the cables I made.