The fact that you've got 2.4Ghz & 5Ghz radios in your router already broadcast on two different frequencies, not networks. It doesn't matter whether or not the SSIDs are the same or not. If I'm reading your question right, you may be getting the terms "network" and "SSID" confused.
I am not a Comcast employee
I have been a Comcast customer since their name was TCI
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