Well, I suspect the path of least resistance is to bring power from the locomotive and use a magnet and reed switch on a tender wheel to generate the chuff. Since the engine doesn't appear to have any chuff switch, synchronized sound with the drivers isn't really an option anyway. Yes, the speed will change the chuff rate based on the tender wheel rotation.
A 2-pin tether isn't a problem, and since we're only dealing with power for the sound, it doesn't have to be a heavy duty wire.
