February 06, 2013, 4:22 PM — Here's how you can stream iTunes music to multiple devices via AirPlay.
1. Make sure your devices are ready and on.
2. Go to the computer you want to stream music from, and start playing a song in iTunes.
3. Click on the AirPlay button next to the volume slider in iTunes.
4. Click on Multiple.
5. Click the device you want to stream your iTunes music to and it should begin playing.
For more, see the original article at the link below.