I'm was wondering, before purchasing the Airport Extreme , if it was possible to connect my 3 Sony Airplay speakers to the 3 LAN Ports of the Airport Extreme and airplay simultaneously as multi-room audio from my Iphone ?
Can you connect multiple Sony Speakers? Yes. Why wouldn't you be able to?
The AirPort Extreme is just like any other WiFi router in as much it is a router, a switch, and a WAP (Wireless Access Point) like any other wireless router.
The Sony speakers are just like any other WiFi speakers in as much they are clients on a WiFi network.
The real question here is does iOS support streaming to multiple AirPlay speakers simultaneously?
Currently, the answer is NO. This is a limitation of iOS.
However, there is an App called Airfoil Satellite which gets your around this limitation.