I think the better solution would be to figure out why you aren't using Media Center for playback and fix that.
Completely agreed. Using MC directly for audio playback would be the best option.
However...
You can set up MC to launch any file it imports via external players as you see fit. You can set them by file-type:
Options > File TypesSelect the file type, or types (note: you can shift-select multiple file types in the list and apply the change at once) and change the Playback Method. You can choose to play them with the Windows-default player (the one associated with that filetype in Windows), a specific external player, or different methods of playback from within MC.
Again, though, I'd recommend against this unless you have a specific use-case that MC can't handle well.