Thank you. Just to clarify, both routers are stand-alone and non-ISP-provided; the cable company only provides the modem. In every other way, my network is functioning well - the only issue has been getting the Tablo to connect to TVs/Rokus that are connected to the router which is not connected to the same router as the Tablo.
Engaging in Double NAT is a big networking no no, but we can help. What is the make and model of each router?