I've started an implementation of a SoundPlayer widget here.
The concept behind the widget is that you place it inside the context of a FileDocument containing a sound file, and it plays the sound upon showing the widget.
It is definitely a proof-of-concept at this point, but it does work! I certainly invite others to contribute.
Right now, the sounds play too often (upon show and hide, every time the widget rendering is updated), and I think it’s creating a new sound manager object each time that happens. Also, the widget parameters need to be cleaned up, and some boilerplate widget code needs to be ripped out.
Perhaps the following snippet can help in your search?
<embed type="application/x-shockwave-flash" flashvars="audioUrl=notification.mp3&autoPlay=true" src="audio-player.swf" width="400" height="27" quality="best"></embed>
Do keep in mind that this was once implemented in a Mx3 project, using a HTMLSnippet that was added to a TemplateGrid. For that specific situation, a notification entity existed, to which users could be linked. As soon as a new notification was added, I believe a microflow timer triggered a refresh of the page/templategrid, resulting in the HTMLSnippet being triggered.
Note that I have not tested the above functionality in Mx5, but the concept could still be applicable, though I admit it would require more work than simply having a microflow trigger a 'play sound event' action.