Example from Kickstarter video (1.01 to 1.15 mins), featuring Eesha Hunjon:
This setup used an iOS app to create the vocal harmony, but we DO NOT recommend this approach for live vocals unless you have additional hardware for controlling feedback.
Using an iRig Pre, a microphone was plugged into an iphone 5 (within the Motion Synth Grip) with the microphone input was fed into the Audiobus app. The Audiobus app was used to host Harmony Voice and Garageband.
The Harmony Voice app received MIDI note commands from the Motion Synth App, and the Garageband app received volume level commands (via MIDI CC messages) from the Motion Synth app.
Within Audiobus, the microphone input was fed first into the Harmony Voice app and that app's output was fed into the GarageBand app.
If you want to perform harmony control live we strongly recommend you use products like the Voicelive Touch with the Motion Synth providing MIDI control. A description of how to use the VoiceLive Touch with the Motion Synth is being created here.
iOS harmony apps will improve if there is demand for them, but at present they need more development before they can match the results produce by hardware like the Voicelive Touch, especially when it comes to controlling audio feedback.