Just got the aircraft, and am struggling through the RXP GTN integration..
1. In the XL560 aircraft folder there is a file called RXPGTN750XL560.exe which you should run.
After that, the GTN shows up in the panel.
2. Close down P3D and go back to the XL560 aircraft folder and edit the RealityXP.GTN.ini file with Notepad, adding three lines if they are not already there:
; is the master device if true.
MasterDevice = true
; aviation db: 0: nav_db2_grm, 1: n