Is there a way to get the GL-X750V2 into IP passthrough mode. Would like it to pass the WAN address to my firewall verse it getting assigned a DHCP private LAN address.
Depends on what you are going to do. In the construction of networks there is no such thing as IP transfer. There is such a thing as routing. Can you clarify your end goal? Then I could suggest solutions.
Maybe bridge mode would be a better use of words. Don’t need to GL-X750 to route anything, want the device to act as a modem and passthrough the WAN IP Address to the LAN interface on the GL-X750, my firewall will perform the routing. Similar to this forum post on this device.
I think here you will find the answer to your question.
Alternatively, you can use DMZ