[SOLVED] Extending a home network where there are two coax hookups?

Mar 29, 2019
I have an interesting network setup in my new place and was wondering if anyone has experience on how to do this. I feel like most problems are about the opposite - one coax hookup and trying to extend coverage across the house. Old place had one floor, so: coax -> modem -> router, done. Simple. My new place has 2 floors, and each floor has a coax hookup. Ideally, I would like to do this:

Top floor: coax -> modem -> router
Bottom floor: coax -> ????? -> ethernet switch (or router, doesn't really matter)

The problem is the question marks in the pattern. I am pretty sure Comcast does not allow 2 modems - especially non-rented - on one account, even if they are ultimately connected to the same line. Considering that this perfectly good coax is right there, I don't want to have to mess around with running cables through the floor, powerline adapters, etc, and this isn't about WiFi range extension. I simply want to extend the ethernet signal from my upstairs modem to the downstairs coax output. Is there some way to do this? Or am I overthinking this and can I just set up a second modem on the second coax hookup with a on the local network and everything will work fine? I don't want to buy a second modem and then have it not work...any advice? I also don't have TV service so that isn't in the equation (and why I would like the switch downstairs to connect my TV, smarthome devices, etc.).