And that code is pretty much what I was doing but will keep my mouth shut before I try it.

Good thing I saved all my stuff before reboot because every darn sketch I'd worked at for the last week or so had it's Whatever.ino deleted from its directory afterwards.
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Will look at again after dark. I have a T2 with 3 buttons and two pots and Din Midi and use it as a workshop Controller/Merger/usb-Midi interface.

With Carlos's query in mind, I'd ducked into it's code as a refresher as I'd left a choice of lines to comment in or out for different modes and had worked out two different ways of doing Merge.