[quote=Ronnie]
B) Most NAS's come with an iTunes Server option built in, so that the above can be achieved without any PC's / Macs being powered on
The iTunes server built into most NAS boxes are iTune share servers and simply appear as a shared library in iTunes. They still need a proper iTunes running on a Mac/PC to server the music such as over AirPort Express.
As long as the two iTunes Library Files (.itl and .XML) are also on the NAS, then you can use the Remote App to "send" Music Tracks to the Airport Expresses [/quote]
Thanks Ronnie for your long posting above which filled in some gaps in my knowledge.
If it's really true you don't need a Mac in each Zone then the cost savings are considerable (if not then per Zone it would get expensive). Can you confirm that with just one Mac, one NAS and multiple Airport Expresses you can control three different zones which are streaming simultaneously?
As VK suggests, the complexity of this relative to other solutions may not be to everyone's taste.