Very beginner question about airGateway LR

I currently have a setup with an EdgeRouter X and a UAP-AC-LR. Everything works like I would want, and I'm very pleased with it's performance.

However, there is one corner of my house where the coverage is spotty, and I would like to shore it up. I have a wired ethernet connection and power available in this corner of the house. I currently have a TiVo hooked up through that wired connection.

What I would like to do is connect (wired) an airGateway LR, power it with a PoE injector locally, and then connect the TiVo to the wired connection through the airGateway LR. Is this even possible? I tried for a very short time yesterday to accomplish this setup, and I got nowhere. I could not get the TiVo to connect to the network through the airGateway.

If this setup is possible, I assume I set up the airGateway with the same SSID, different channel, adjust the power of it and the existing AP, and I should get some pretty decent roaming from one AP to the other?

Or is there a completely different way I should be thinking about adding APs to my existing network?