Equipment Upgrade Question

Hello… I recently received a notification through the Xfinity app that I was due for an equipment upgrade. I received a new gateway and two new TV boxes that are Wi-Fi only.

My current set up before the upgrade is I have a primary box that is wired with a cable as well as a secondary box that was wired with a cable.

My question is… Do I need the primary box to be wired directly with cable to make this work? When I disconnect the primary box, my Internet goes down therefore it makes it impossible to set up the Wi-Fi boxes. 

Any help would be greatly appreciated!