Sorry for the confusion Phil, I was replying to the post relating to the iOS version of iReal Pro, not Mac OS X. It was wrongly posted in this forum.
To import the audio file using OS X version:
Set the player settings, key, number of repeats, mixer volumes etc. for the song
Share (top right)>Song to WAV
Choose a location to save it in
Open GB, set up a song
Then simply drag the song file into the timeline (it seems to create a new track for the file)
I hope this helps.