Cincinnati Bell → FiOptics behind two routers

I have been using FiOptics internet 30/10 for a few months with no problems. I was running my own Subsonic Music Streamer, Plex Media Streamer, and a Splashtop interface that i have configured to work with port forwarding. All this was done using a Cisco E3000 router going directly into the ONT panel.

The problems started last week when I upgraded to FiOptics TV. According to the install tech, I have to use their ZTE Modem/Router and I'm no longer able to access my Subsonic, Plex, or Splashtop servers outside of my network bc the ZTE nullifies my port forwarding. If I setup the DMZ with the ZTE, it'll successfully forward the ports but then my FiOptics TV won't work (the tv will work for about 30 seconds and then freeze up with a 'loss of signal' error message). I believe this has to do with the feed switching from the unicast to multicast. If I disable the DMZ, the FiOptics TV will work, but none of the servers can be reached outside of the local network. Any suggestions on steps I can try? Some previous posts indicate some have had luck with bridging the ZTE. Others have mentioned IGMP Proxies. I think the E3000 supports IGMP Proxies, but will confirm this evening.

Here's a crude explanation of my setup after the install
Fiber -> ONT -> ZTE Coax-> Splits TV to Coax (Cat5 is not an option atm)
-> ZTE Cat5 -> E3000 Router (For Wireless and gigabit NAS)

I appreciate any help you can offer. Cincy Bell support has been a dead-end.

They lie when they say you need the router they supply. They just assume you don't know what you're doing and the techs are probably required to install the router. Plus it's an excuse for them to charge you a monthly fee for using it.

If your own router supports IGMP proxy then you can eliminate the ZTE from the equation.

On a side note, technically you should be able to port forward through two routers (I've done it), but it's not ideal.

The house is wired for coax, but not cat5 to reach both of the STBs. If I remove the ZTE from the equation, would I just need to add a MoCA adapter? If so, at what point of the chain would the MoCA adapter go?

I have stock firmware on the E3000, so I'm not sure if it supports IGMP Proxy. All the documentation that I could find refers to the hacked firmwares for the E3000 (Tomato, DD-WRT, etc)

Ideally, I'd like to remove the ZTE as it's a pain, takes up too much space, and tends to run hot.

Yeah, all you would need is a Moca. You'd plug it into your router's LAN port through Cat5 and then your STB's are fed through the coax from there. It's too bad they forced the ZTE router on you with the built-in Moca, because they do supply stand-alone Moca's and use them in certain setups.

AFAIK your E3000 supports IGMP proxy/snooping and it's enabled by default. You'll want to make sure that "Filter Multicast" is disabled in the firewall settings if you enabled it (having that enabled disables multicast traffic). The language they use to describe this setting has been pretty confusing over the years.