How do I stop my AirPort Express from showing up under AirPlay?
Uncheck AirPlay
Goto the the AirPlay tab in AirPort Utility and uncheck 'Enable AirPlay'.
Reboot all AirPlay playback devices
To ensure that you will be able to wake output AirPlay devices through the Airport router reboot connected output AirPlay devices.
Also, the connected AirPlay device might have to be connected through ethernet for it to be able to wake from sleep when video/audio is sent to it.