Yeah, this is why it's confusing. The cable company and everyone else throws terms around too casually and imprecisely, and then everyone's confused.
The Surboard 5101 is only a modem, not a router. It has no firewall or any other protection whatsoever. When you connect a device to it, it gets assigned a public IP. And that's exactly what happens when you connect a router to the cable modem. The router's WAN port gets assigned the public IP. The router then creates a *private* network (e.g., 192.168.1.x) behind the WAN so you can share the one public IP. The router also provides a firewall for all those devices on the private network.
Likewise, the DPC2203 is only a cable modem, not a router. And for all intents and purposes, works identically to the Surboard 5101.
So as far as I can tell, I see no routers at all in this configuration, which means you have no ability to share your internet connection. All you can do is connect a single device to each cable modem. Not necessarily a problem if you only have a single device (e.g., PC), and if that device has its own firewall, but it gets expensive adding cable modems each time you need to provide internet access to another device. And as I said, those devices must provide their own firewalls (unlike your PC, the magicjack probably doesn’t). That’s why we have routers! Routers let you share the public IP associated w/ each cable modem, whether wired or wireless, and provide protection via their firewalls.