You can achieve open nat with this router via standard and 3rd party firmware.
Keep your normal uPNP enabled; this should handle the 1st xbox one. The following is for the 2nd xbox one in your network.
Use static IP settings on the router or xbox one; doesn't matter just know your 2nd xbox one's ip.
Then port forward to sub-standard external port then map to standard internal port and forward to your static ip.
This can technically be done on most routers, so it's not really exclusive to this router.
I attached a screenshot of my port settings. I have blocked out anything not pertaining to XBL. I may be missing a few ports so if you have any more to add for 360 or One send them my way. Now; notice I have a block of port numbers I'm using for external
ports(6668-6676); then I map it to the proper XBL internal ports and forward it to the 2nd xbox one's internal ip address. I am running tomato firmware however as I mentioned you can do this on pretty much any router; I have done this on the stock WRT-54G
firmware also. I have open nat on all my xboxes.
[View:https://onedrive.live.com/redir?resid=C58FCF2EA689879C!5804&authkey=!AOKp5q2OZvp6Zz4&v=3&ithint=photo%2cPNG:0:0]