Wired backhaul of RBR50 & RBS50 directly to ISP's modem/router

Oh it's working, I just got my friends going yesterday. 

https://community.netgear.com/t5/Orbi/Orbi-firmware-update-v2-1-4-16-availability/m-p/1592753/highlight/true#M34020

Whats the mfr and model# of your ISP modem? 

Modem Combo Units:
Couple of options,
1. Configure the modem for transparent bridge mode. Then use the Orbi router in router mode.
2. If you can't bridge the modem, disable ALL wifi radios on the modem, configure the modems DMZ for the IP address the Orbi router gets from the modem. Then you can use the Orbi router in Router mode.
3. Or disable all wifi radios on the modem and connect the Orbi router to the modem, LAN to LAN and configure AP mode on the Orbi router.

I would do this, disconnect ALL other devices from the router, accept for 1 wired PC. 

Add the satellite first via wireless. After it connects with a BLUE led on top, then connect a good quality LAN cable between the satellite and router. Do this with the satellite and router close. Wait 5 minutes for the system to reconfigure the new connection. Top LED should go Magenta then turn BLUE. Check internet from your wired PC thru the router. Should have internet. Then you can connect the wired PC to the back of the satellite, should have internet. If good here, then place satellite at final remote location. Power ON satellite and after connecting LAN cable there. Lan cable at remote location needs to be connected to back of Orbi router, not ISP modem. Wait for BLUE led on top. SHould go BLUE. Check internet connection with something connected to satellite here. If good, re-connect all of your other devices to the router and such.