Looking through the cast-web topic on the SmartThings community and poking through the limited help articles they have, it looks like it’s possible to play publicly hosted MP3s and it sounds like if you put those into a playlist, you could play the playlist as well.
The cast-web topic in the SmartThings community is probably going to be the best place to ask questions about that device handler:
Once you know what commands to send the device, you can create a rule in the SharpTools Rule engine and then run that rule directly from your dashboard similar to this thread:
I don’t have the SmartApp/device installed, but it sounds like they also have some concept of presets that might be useful to you: