Once more thing: I’ve modified (again) the jacknetumpd service to include support for client mode. Now, you can run it with the option --host, and it will try to initiate a session with the given hostname (or IP address). You can also set the --port to a given number (by default, it is 5504), and also the --endpoint-name (by default, “Zynthian UMP”). Once connected, you can use it locally through its in/out Jack ports. If no option is given, it will work as before, waiting for another peer to initiate a session (server mode).
For example, to connect to your Zynthian from your Linux machine, run:
jacknetumpd --host zynthian.local --endpoint-name $(hostname)
This changes are available from release v1.3.2 onwards. I’ve added a Debian package for both ARM64 and AMD64, here:
Btw, everything was there, in @BEB’s NetUMP library, I only made it available 
.