Something I've run in to, and haven't been able to find a work around, other than shutting one app down so the other can work.
If Opera is up and running and I view a video (like Youtube), then try to start Amarok, it states that the playback device isn't working. Reverse also results in a video without sound. If Amarok is running first, and then I attempt to view a video, there's no sound. Suggestions?