You could also possibly port forward. But anybody who types your home network address could have access. You could probably I stall nginx along side of fpp like I have with my openhab home automation setup for secure access. Not sure
You've got multicast selected. I use unicast with each output on advatek assistant matching xlights. So xlights will have 16 controllers listed. Not sure if its the best way but it works for me
I don't know how the whole matrix and 3 nodes per channel work. But in advatek you have output 1 and 2 both starting on universe 1. Click auto sequence channels bottom left. Set output 1 to be start universe 1 with 1 universe. Output 2 start universe 2 with 1 universe and so on. And make xlights...