I love Runeaudio

Maybe this feature already exists - or it is possible with a simple workaround

Lets say I play audio Files from a playlist or webradio.
Then my KNX home automation System detects that the dishwaher finished - I would like to trigger an audio file "dishwasher finished".
This would be nice with a fade in and a fade out.
Music should play all the time.
Like if you have a TomTom at your car and the voice comes to your speekers while listening to a radio station,...
How can I do this?
GreeT`s Erich