OK! I like the idea of reserving a MIDI channel for controlling the Zynthian UI.
@mheidt, why do you prefer the channel 14? Channel 16 seems the logic choice ...
In the other hand, I think that the better way of avoiding problems with snaphosts using the "zynthian master channel" in some layer, is not allowing to use this channel, removing it from the list (asumming the master channel is fixed and not easily configurable).
Also, i like the idea of configuring the master control messages from the web tool. It's an easy task
Regarding the "master volume", i've seen that GM2 defines Universal SysEx commands for this (also for scale trasposing and tunning).
What do you think? Should we implement GM2 or go our way?