I've been looking online, and it seems that the Cisco XB3 DPC3941T is actually a Modem with wifi built in and not a router. This means that settings that a router would have (Like QoS) don't actually exist on the system. Hopefully, this means that you don't have to worry about QoS, as it is designed to strengthen a service's bandwidth (like online gaming) when other services (like updates to a computer or phone on WiFi, skype calls, etc.) are trying to be used. I thought this had become standard, but maybe Modems aren't part of that change.
If you'd like more control with your WiFi's configuration, then getting a router to handle your Wifi would be ideal (though pricy since you've already got WiFi access with your modem). If you've got it hard lined, then with the ports open in the url above and uPnP on you should be ready to go. Happy Smashing!