Cannot change Wifi channels; system is managed automatically

what comcast gateway do you have? I was able to that on every rented comcast gateway until i got the new Xb7

I have to new modem/router.  If that is Xb7 then that would explain it.

For what it's worth, did you try to modify settings thru the Xfi app or connect thru

http://10.0.0.1 admin panel? Just in case you have the Xb6 gateway I was able to access some basic settings in the admin panel >connection > WiFi 

@CCAndrew  I spoke with comcast advanced repair for over 4 total hours this week trying to un merge my 2.4 and 5 GHz bands and they finally landed on I would need a different model that does not automatically do band steering like the one they provided me does. I appreciate your response that confirms I need my own router (and wish I had looked here sooner). My question is can this router be found through comcast services or should I go outside of comcast equipment products for this?

Normally I would say get the best Netgear router you can afford however, in the last months there have been developments in other manf routers that may be better.  The only reason I went back to Comcast router is that the tech changes for now are coming so fast that keeping up was becoming an issue; it could be that within a year I may go back to an OEM router but at this time I cannot recommend any particular manf.

You can go here to find compatible equipment:

https://www.xfinity.com/support/devices/

Then buy it wherever you choose.  (With some caveats about buying potentially used modems at places like ebay – sometimes they turn out to be rentals/stolen and you won’t be allowed to activate those.)  I got mine at Costco.

There are only straight cable modems and combination modem / router gateway devices at that link. They don't classify stand-alone routers. If you want to use a stand-alone router along with a straight cable modem, then anyone will do.

Asus makes very good routers ! Good luck !