You might want to check into the Squeezebox line. See http://www.logitechsqueezebox.com/. I use the Touch model in my main system. The server is in the basement and contains over 46,000 songs. One can assemble playlists in any order and add to or edit them as you're playing other songs. The ability to access and search your music library is amazing.

The connection between the players and the server can either be wireless or ethernet cable. The Touch player can be controlled from its screen, or from a remote or laptop.

One music server (actually just an ordinary PC) can support multiple Squeezebox players. I've got a second system that uses their SB3 player and the "Radio" model in the kitchen. The players also support internet radio.