You may or might need multiple outputs from the 750.
1. You need a serial line out from the 750, in to the HXr, for gps data. Both ports should be configured for "Aviation" and set to 9600 baud.
2. You may have a line from the HXr, to the 750, to transfer data to the 750. Set the HXr to "fuel air data Z format". Set the 750 to "Shadin FADC". Both ports to 9600 baud.
3. If you have a 2020 approved ADSB-out device, the 750 can serve as an approved position source if your ADSB-out can accept Garmin "ADSB+" format.For example, the Garmin 330-ES, the Trig TT-22 and TT-31 mode S-ES transponders can all read this format. Run a wire directly from the 750 to the transponder, set the 750 output to "ADSB+". (Note: if you see "ADSB" but not "ADSB+" as an option, you need a software upgrade to the 750.)
Hope this helps.