It isn't immediately clear how to play audio in Avlaon.  Basically, anything Windows Media Player can play can be played by Avalon.  Here's some sample code that could be wired up to an event:

MediaTimeline mt = new MediaTimeline(new Uri(@"C:\Documents and Settings\All Users\Documents\My Music\Sample Music\Beethoven's Symphony No. 9 (Scherzo).wma"));
mc = mt.CreateClock();