Honestly, if you want to get out from under Comcast's thumb, replace router modem. You can have all the other devices you like (Switch, Router, etc.), but the main connection and control of that connection happens at the modem. There are Comcast compatible modems for sale on Amazon and they are not expensive (I bought one and it works great!). The type of modem you need to purchase depends on what services you have from Comcast. For example, if you have Comcast Voice, you will need to get a modem with Phone port (rj-11), as well as the normal Ethernet (rj-45). This is the modem I have, it does not have a Phone Port, but this one does.
In the end, purchasing a modem to replace Comcast's will save you the monthly rental fee they charge you, give you more control over your network and hopefully out-preform Comcast's. Hopefully it will open up new ways of being able to get the setup you want. Good Luck!
P.S: Comcast Modems are actual Modem/router combos so you technically have 2 routers including your Cisco one. Turning the modem into Bridged Mode basically just removes the router.
Pic of My Modem
Since you have a router externally as well, there really is no need for 2 routers. That's where literal signals get crossed. I am sticking with my original recommendation to save yourself some money and take back control of your network. (Notice Xfinity's Modem has several important options greyed out)