In Combi mode, playing the mini keys directly in the app uses the Chord option just fine, but not with an external keyboard (Xkey 25). Can't seem to work out how to set this up - anyone here give this a shot with any success?
Most likely. The nano series of controllers probably doesn't send standard MIDI over USB, at least not in a format that any MIDI-compatible app can work with without having proper drivers installed. If possible, I'd see if you can try it in store or find someone local who has one and try to get it ...