I have just been experimenting again with iOS audio. This involves using a simple sound generating app with an AudioDeveiceSelectorComponent. If you set the number of active input and output channels to zero, you hit an assertion from here . . .
floatData.setSize (numInputChannels + numOutputChannels, actualBufferSize); // <-- setSize doesn't like this to be zero
zeromem (inputChannels, sizeof (inputChannels));
zeromem (outputChannels, sizeof (outputChannels));
Easily fixed with this (or similar)
floatData.setSize (numInputChannels + numOutputChannels, actualBufferSize);