Since they have an air whistle, it should be easy to remove that and install the ERR RailSounds Commander. You already have track power, and since these are obviously conventional locomotives, that's all that's required. If you want chuffing sounds, you will have to install a chuff switch, usually a magnet and reed switch on one of the tender wheels. All of this comes in the ERR RailSounds Commander kit.
Go to this Link and then look at the RailSounds products: The Electric Railroad