I did a quick look at the Arris TM722 modem and it had the same issue as my previous modem -- only one ethernet port. That is why I asked Comcast to replace it with a multi-port modem (I have the Cisco DPC3939) so that the Netgear XHS router can get it's own internet port and not clog up my home network. Call Comcast and request they swap out your modem so that you have one with the multiple ethernet ports.
The tech that came out to do my swap said that eventually the newer modems will be able to be configured so that XHS can happen without the Netgear POS. I plan to follow-up about this in a few months.