To get an audio interface working with iOS apps the audio interface must support CoreAudio class compliant drivers.
This means that the manufacturer of the device must implement that, the programmers of the app can't do anything about it if the device does not have class compliant drivers.
Also, not every audio interface can support CoreAudio class compliant drivers. You should contact the manufacturer of your interface to see if they will support CoreAudio class compliant drivers.
Carlos Rohde - Product Marketing Manager Cubase & Apps
Steinberg Media Technologies GmbH
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