Now it appears to work, when I made the Cue sends stereo. This is a waste of outputs, and something that Steinberg really needs to look into. Mind you, this was one of the first things I tried and it didn’t work the first time around.
Now there is another problem though. It’s a bit of a hit and miss affair whether the “MR816 Hardware Setup” option shows up in the “Devices” menu at all. The most I’ve had to relauch Cubase to get it to show up, is 5 times!
Clearly there are some compatibility issues here, that need to be looked into.