Although Bento allows you to play audio files in the background, At this time, FileMaker Go cannot. The Container field switches to full screen.
I recommend that you enter this feature request into our Feature Requests web form at:
The entires into this web form are automatically populated in a database file that is monitored and read by Development and Product Management, where the suggestions are then discussed and considered for possible inclusion in a future release. Be sure to mention how this works in Bento and provide the same example why you need this. Although I could copy your post into the web form, there are a couple of questions asked that only you can answer.