How to set kAudioUnitSubType_Distortion
Admittedly, I didn't know anything about your issue before, so I did a little bit of looking at your code, and at Mac Developer's CoreAudioOverview.pdf which led me all over the place. I didn't see anything too sneaky going on in your code. It looks quite tight, but I did wonder about these lines:
// set effect unit asbdAudioUnitSetProperty(effectUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, &audioFormat, sizeof(AudioStreamBasicDescription));AudioUnitSetProperty(effectUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 0, &audioFormat, sizeof(audioFormat));Most particulalry why there are two lines here. Should you not just have the first line?
Just a thought.
If that is of no value, then, have you checked to make sure that your audio graph is all connected properly. And also can you try a different effect and see if that works?
Good success on this project. CHEERS!