Okay, I was assuming the VoiceLive was acting as a real audio interface, which would enable the possibility of multi-route audio. But if it's just taking the iPad audio from the Lightning jack, that does disable the headphone jack and there's no way apps can change that behavior. To work around that, you'd need to connect a USB MIDI interface between the iPad and the VoiceLive rather than using a direct USB connection (or use the wireless MIDI interface as you suggested).