For some reason, the MC6 doesn't communicate with the Zoia. It looks like this is a known issue, as Empress offers a fix that requires replacing a chip on the motherboard:
That took a bit of digging to find, and is one of the only things I could find online about this issue... but I have no idea what the actual issue is. I plugged the MC6 into a PC with MidiOx and all of the commands were being sent well. I plugged other gear into the Zoia and it responded. I looped the MC6 through MidiOx and echoed the output to the Zoia and everything worked as it should.
I even set up an old 2-in, 8-out midi merger/filter between the MC6 and the Zoia, and everything worked perfectly. It looks like the only thing that doesn't work is connecting the MC6's output directly to the Zoia's input.
I'm baffled... but I don't want to take a soldering iron to a pretty expensive Empress effect. Does anyone know what causes this and if there might be a workaround?