Have you looked at the Logitech SqueezeBox? There's also a software version of the player called SoftSqueeze that is free to download.
Basically, you install some server software (SqueezeCenter) on one computer and install SoftSqueeze on the client (they can be the same computer if you like). Now you can access all your music all over the house, and best of all, you can synchronise all of the streams if you like. You can add (relatively cheap) stand-alone hardware players too if you like.
(I'm not sure if this is what you're looking for, I found the original post a little hard to read.)