WAN Aggregation on XB7 Router

So my experience on this topic as i have a Xb7 and asus RT-ax86u, so i use the dual wan setup, not the wan aggregation, the problem with the asus routers is that even if they are multi gig, one can only access the 2.5 gig port on the lan or wan side, not both at the same time, so that obliviously that an can be a insurmountable problem if you don't think outside the box, so i leave the xb7 in the standard mode not bridge for this to work, so for the dual wan to work properly, it needs to be fed 2 1000 Mbps connections via ethernet ports, the xb7 in standard mode does this perfectly, don't even bother with the 2.5 gig red port , so by delegating the lan side to 1000 Mbps, it then leaves open the option to configure the wan port to use 2.5 gig, it also leaves the red 2.5 port open for other purposes , as some indicated this setup creates double Nat situation, so use that to your advantage, so i now have 2 subnets, 10.0.0 and 192.168.50, so obviously they cant  communicate  with other,  so again use that to your advantage, so i can have the xb7,  in full default mode, single wifi name, managed automatically, works great, so i have two network printers installed on each subnet, so you see where might be a issue printing, so thinking outside the box, i connected to both  subnets  simultaneously, so i am issued a IP on each subnet, have a default gateway on both subnets,  so when i want to print a document, i am giving the option of both printers, beautiful, so i see folks wanting to split the wifi bands for whatever reason, they cant because they are using pods etc, so why not connect the rouge device to the other subnet, it will be issued a IP not associated with the xb7 10.0.0, again the double Nat issue, so depending what devices you need to freely communicate with other, arrange them on the appropriate subnet to make that possible, my main computer i can access both subnets as explained above, so is this ideal, i seriously doubt it, i am sure if you run a elaborate network there will be numerous pitfalls, i myself don't have a fancy setup, There are many other ways to set things up, sorry for the rant....

Thank you for the thorough answer. I can deal with the double nat (or triple as I have two different routers behind my setup). I'll give it a try and see what results I get. 

My setup would be as follows:

2 x 1 GbE - Bridged to ASUS Router

1 x 2.5 GbE - Connected to Motorola 2.5 GbE MoCA 2.5 Adapter -> Linksys Router

Use one of the remaining ports on the XB7 for the network laser printer so it can be reachable by both networks.  

Keeping the two routers split off the XB7 would result in two double NAT networks.

Here is one point I forgot to mention, so the Xb7 default config don’t allow for any static Ip to be added, you can add reserved ips tho, if you look at the dhcp server, the dhcp server range starts at 10.0.0.2 and ends at 10.0.0.254, so there obviously isn’t and open Ips, easy fix, how many do you require? 100? Just edit the the dhcp range to start at 10.0.0.100, you can also add it at the end if you prefer, I’ll look into the port forwarding issue, I don’t use it now, but I was wanting to play around with it at some point, maybe give me a hint why it isn’t working or maybe a error message