Barix http://www.barix.com/startseite.html makes the instreamer and exstreamer products, this combination is great for connecting audio to multiple transmitters in time sync. In the past the most common way to provide the audio connection was wide bandwidth phone lines, which are expensive. Some have used Part 15 microwave links with some success. People also have been using the Internet to provide the link, but time sync has been an issue. Now with the sync feature Barix offers a network can be setup efficiently. I believe that Barix offers a wireless model so all one needs is wireless internet at a proposed site and you are good to go! Plus these devices are reasonably priced.
There are other internet based network players out there but barix is the only one that offers a sync feature. http://www.slimdevices.com/