disable modem in C7000

I would like to disable the router in my AT&T cable modem/router and use the router from my C7000 for both wired Ethernet and WiFi.  In the past I had an ISP where I could use this device as my modem/router.  Now .. I am forced into using an AT&T modem.  The router in the C7000 is much better than the AT&T router, so I would like to use the C7000 as my router for both wired Ethernet and WiFi.  Do I have to disable the modem side of the C7000, or do I just connect one of the 4 Ethernet ports on the back of my C7000 to one of the Ethernet ports on the AT&T router and disable the WiFi in the AT&T router to avoid radio interferance?  I would like to disable the router entirely in the AT&T device so I am not adding latency from passing through the AT&T router.  If so, then I can contact AT&T to disable the AT&T router.