Wanted to post this new so it wouldn't get buried in another discussion:
I found a conflict between GB and A4+, specifically: Using GB's inter-app recording feature while plugged into the A4+ interface introduces distortion into the recorded audio. I had thought my interface was malfunctioning somehow. IC support suggested using AudioBus: this solved the problem.
I don't know if this problem is related to my particular iPad model (iPad Air 2). If, however, you encounter this problem then try AudioBus for inter-app recording.