The Android Roon Remote, you can manually enter an IP. My Android phone is on a WiFi with one subnet, the Roon Server on another. So that works. No need for the same subnet!
Then why should one not be able to tell the server to scan IP x.y.z.n to find a bridge
I can probably make an ssh tunnel from the RPI-Volumio to a host in the Qnap-Roon-Server subnet, that would work, but I would rather not!
See the following post. I can move the thread to #tinkering if you like since this isn’t a supported configuration but there are some who have got it working.
Welcome to the forum. As @Martin_Webster mentioned, we can only support Roon when Core, Remotes and Endpoints are on the same subnet. Since you have multiple subnets set up, you are in #tinkering territory, and I have moved your post over to this sub-section.
There are a few threads on the forum of users who managed to get Roon working on a non-flat network if you search around, but as I mentioned, these are not officially supported and you’ll have to try and see what works yourself.
Roon uses multicast for endpoint device discovery, and remote to Core connections, so a few have mentioned the need for an mDNS reflector: