If you are using LearningWare Gameshow Pro 3 (PS/2) transmitters, click the drop-down and select LearningWare Gameshow Pro 3:
Note: You do NOT indicate which Leader Transmitter is facilitating the game. After selecting LearningWare Gameshow Pro 3 as your transmitter system, AllPlay automatically knows which transmitter to designate as the Host/Leader Transmitter.