Tasker is overkill for your request but you might want to look into it anyways as it can automate nearly anything and you'll probably be wanting to do some more advanced stuff eventually anyway.
specifically use the action type Alert > Notify Sound to play the MP3 based on whatever rules you want...
or you could have Tasker even call the Audio Glow app with a certain intent to tell it to "press the play button" - but only if the app was designed with a receiver for that type of interaction (what's an Android intent?)
EDIT - sorry i didn't realize that Automagic was kinda like Tasker - if it can send intents then you just need to find if Audio Glow has a receiver for a play intent, look at apps like Package Explorer or Intent Intercept to try and find that out, or just email the Audio Glow developer! most developers are willing to help out with reasonable requests.