216 views and still no comment from Apple or any other user. I think there is no way to enable that functionality in the Mac version of the app. So I will remove that option in the next version for Mac.
Here is a workaround how to achieve the same on the Mac:
- Open the Audio-MIDI-Setup app
- Go to MIDI Studio > Open MIDI Network Setup
- Follow the steps in this screenshot:

When you quit Stage Traxx you will have to reconnect it in the Audio-MIDI-Setup app.