This is how I print VI's to audio:
- create a new audio track, and pick a free bus as the audio input
- create a pre-fader send set to unity gain on the instrument track routed to the same bus as above
- mute the instrument track
- record-enable the audio track, and hit record
Muting the instrument track has no effect on the recording, but ensures that you're only listening to the printed version of the VI.