CasaTools Multiroom Music Server
The interface on this device looks pretty good and it’s quite expandable, but the price is definitely more than the casual user is going to want to spend.
The CasaTunes XLi Music Server ships with four built-in internal music
sources and one external source for up to six rooms of music listening.
The XLe has five built-in sources and four external for 12 rooms; it’s
also scalable to four external boxes for 48 rooms filled with music.