I was a bit confused on how to use this. I enabled a few LV2 MIDI Tools in webconf then added a MIDI-FX Layer on channel 3: #3 JV/MIDI Keysplit. I see that ZynMidiRouter channel 3 is connected to MIDI Keysplit’s input but its output is not routed to anything. It took me a while to figure out you need to use the MIDI Routing option in the context menu of the plugin to route its output. I guess it is just me not being familiar with it yet. I guess we will see something in the docs soon…
It is not clear how to match the MIDI channels. You select a MIDI channel for the MIDI-FX Layer and it will generally listen on that channel so when you route it to an instrument that must sit on a different channel, the instrument will ignore the MIDI-FX chain (wrong MIDI channel). I guess there is something you can do with clone or rules but I would like a simpler solution.
But we do now have a way to add keyboard splits within the Zynthian which is cool and has been requested in the past (here and (here).