I’m not sure that a cable modem behaves the way a DSL modem from AT&T does. I’ve only ever worked with cable modems and i’m not aware of a bridge or DMZ mode. It’s mostly a plug and play closed black box affair.
My only advice is buy your own DOCSIS 3.0 cable modem and tell WOW! Cable to shove their shitty box right up their arses. I know Comcast charges 7 or 8 dollars a month to “rent” their cable modem that by default comes with a public WiFi network turned on. Not to mention its bottom tier garbage. Get a Motorola Surfboard modem, i’ve had mine over 3 years and nary a hiccup out of that thing. Plus its ONLY a modem. No modem/router/AP/switch frankenstein garbage.