Hello @Matthew_Partrick,
I am not too familiar with Comcast routers, but the option to add devices as firewall exceptions can usually be done in the Router Settings page. If you can provide a screenshot of how you added Roon as an exception, I may be able to provide more information but as I mentioned, not too familiar with those types of Routers. I have found this documentation which may help: https://www.xfinity.com/support/articles/advanced-xfinity-wireless-gateway-features, generally speaking you add the Nucleus’ IP address to the exceptions page and these ports to allow the connection: Can’t find Roon “Core” from Remote. Hope this helps.
Thanks,
Noris