MainStage 3 output routing

I am trying to use my Steinberg UR28M audio interface with MainStage but am having some difficulties. I'd like to be able to route the various tracks in MainStage to the outputs on the audio interface, i.e. sending Playback 3 in MainStage to output 3 on the UR28M. Is this possible? I've been trying hard to make this happen but can't seem to find a solution.