The Linksys WMLS11B Wireless Music System has been boxed up and returned after a few more fruitless hours of testing.
The replacement is the Netgear MP101 Wireless Digital Music Player. There’s no built-in speakers but powered speakers are cheap and easy to come by. Netgear’s server software is far friendlier and less buggy than the lame version of MusicMatch required by the Linksys. I had the Netgear device up and running within fifteen minutes. Your mileage may vary.