Router/modem with 2.4 frequency

Does Xfinity rent a router/modem that 1) supports a 1GB speed, and 2) allows manual override to specific frequencies?

I recently upgraded to a 1 GB plan and received a new router modem. It is my understanding the model I have has multiple banded frequencies and is automatically determined and cannot be overridden. I have two devices that require a 2.4 connection and will not connect to this router. I realize I can purchase a third party router and modem with this capability but I have also seen comments and reviews that even so-called compatible devices have not insignificant connectivity issues with little tech support provided.

i am willing to stay with a rented router modem if it can meet the two conditions above.

thanks