Time Out will list system sounds, or sounds in the Sounds folder within the data folder. The easiest way to get to that is to choose Reveal Themes in the pop-up menu on the Break Appearance page, then look at the adjacent Sounds folder.
You can then play the sounds via the Play Sound action, and even have them fade out later (e.g. at the end of the break) via the Fadeout Sound action.
See this related blog post for more information.