Cannot Disable DHCP Server on the new Xfinity XB8 Gateway

I just purchased a Firewalla Gold Plus and have a new Xfinity XB8 gateway (router/wireless/ethernet) with the new second generation XFi Pods to create a mesh network for a large 2 story house.

I have spent hours on Xfinity chat/tech support, Google, Reddit, etc. and I find that I cannot disable the DHCP server mode to allow the Firewalla Gold Plus to be the DHCP server. Their only solution is to use it (the XB8) in Bridge mode, which completely disables the routing, but they have these disclaimers for putting it in Bridge Mode:

"The Xfinity Wireless Gateway puts the technology of a modem and router into one piece of equipment, creating the fastest, most reliable in-home WiFi.

We understand, however, that there may be times when you may want to use your own router.

To do this on our network, you'll have to enable the Bridge Mode feature on your wireless gateway, which turns off its routing capabilities while leaving the modem capabilities on. Then, you may connect and use your own router.

Note: Any ethernet port can be used but only one device can be connected to the gateway while in Bridge Mode.

When Bridge Mode is enabled, you can access the Xfinity app to manage your account, but you won’t be able to use Xfinity xFi and xFi Pods features to manage and personalize your network.

If you're a customer with xFi Advanced Security, you won't be able to access this feature if you choose to enable Bridge Mode on your gateway.

In addition, if you already activated xFi Pods, you won't be able to enable Bridge Mode."

I want to be able to use all of the functionality of the Firewalla Gold Plus, including the 2.5GB ethernet port connection to the gateway.

I saw the article in Firewalla: "Setup Guide: Routers that are not able to turn off DHCP Service" and the screenshots look almost identical to my gateway on the XB8, but there is this message:

"Notes on IPv6:  
Some providers don't allow the router to fully disable or limit IPv6.  When this happens, Firewalla will not be able to manage any site that's IPv6.  Resulting in you can't see traffic or block any IPv6 sites.  We are working on a solution, this may take a while.   For example, if you block Firewalla.com it will work, but block google.com will not."

Is this a problem? Is this the case with the XB8? Is this the best workaround for the XB8's inability to disable the DHCP server mode?

Any help here would be much appreciated as I really want to keep and use the Firewalla Gold Plus router for security and monitoring.

Thanks!

Chris