here is an example of controlling a large pd external. Paul streach is a sound tool that can streach out a sound to years in length, producing a smooth like drone quality.
Simply i have taken the external, added a volume slider, and given it a folder of sounds to choose from. I could go on and put presets on it,do something with the pan, put it thru a fx unit. then get it to auto-start turning the pi into a wierd timestreach instrument