Comment 13 for bug 1297790

For those who really want to get rid of the dialog in the meantime, here is what I did in order to quick-fix my own system. I made a simple hack, and followed the steps listed here to rebuild the unity-settings-daemon package

https://help.ubuntu.com/community/UpdatingADeb

The hack (to be done in place of the "patch -p1" step in the guide) is to disable the new functionality; I did this in a possibly very inappropriate way, please don't blame me too much. I edited the file unity-settings-daemon-14.04.0+14.04.20140414/plugins/media-keys/what-did-you-plug-in/dialog-window.c and added "return 0;" as the very first line of the function wdypi_dialog_run. There may be better ways.

My two cents on the solution is to chose a fallback, issue a notification, and allow the user to configure the default behaviour in the audio settings. That would be less in the way.