“The Sound Blaster Wireless Music is a small receiver module that plugs into the analog line-in or optical S/PDIF inputs of a home stereo or powered speaker system. Its built-in interface lets you use the included remote to browse, organize, download, and play MP3 and WMA files stored on the network-attached PC of your choice. You can wirelessly connect up to four output devices (speaker sets or sound systems, each requiring its own module) to a single PC on the same network.”
This review from PC Mag is pretty strong. I want one!