Is there a maximum number of AirPlay receivers that I can output to at the same time? If I buy 6 different Airport Express' to have one in each room will they all work together or is there a maximum number of receivers you can use at once? For example if I want to choose between the six rooms or play the music in all the rooms at once will that work?
The maximum number of Airplay receivers are 3 to 6 as noted in iTunes: About playing music with AirPlay


  The maximum number of outputs are three to six in typical conditions. The number that works for you will depend on your environmental conditions (such as building composition and local radio interference), distance to the outputs, and available network capacity relative to your other usage.