Trying again ...

I posted this a few days ago but didn't get a response - at least not one that helped me.  Thought I'd try again ...

Is the below true?  I need a dedicated 2.4 GHz network.  I use Xfinity's XB8 gateway (supposed to be "the best" for xfinity customers).  I have 2 devices that will not connect to the gateway and the commonality is that they require 2.4 GHz connections.  Both are in my garage (garage door opener and sprinkler controller).  Do I need to replace the XB8 with my own device?  

To net it out, I'm pretty convinced that I can't setup the XB8 gateway to have a separate 2.4GHz network.