I listened to the Geek News Central podcast recapping CES, and it mentioned Oyster Speakers. It sounds like they will be coming out with speakers that will get the audio from a 802.11 signal. They mentioned that it is possible to use them as a stereo setup, or in a surround sound system.
They mentioned that the speakers would be available later in 2006, and would be about $500 for a pair. This would be a lot cheaper than the Polk Netstreams speakers.