I had a similar problem to the WBUR listener in another thread -- my local NPR station broadcasts MP3, but only in 16Khz, which Sonos will grudgingly attempt to play, but it doesn't work very well.
So I did some fooling around on my linux machine, and managed to produce an icecast stream reesampled to 128k at 44.1Khz. I can go into more detail about how that all works if anyone is interested. It's pretty kludgey at the moment, but I'm just trying to figure out what's possible. In theory, this would work for just about any stream, since mplayer can produce PCM audio from lots of formats. My stream uses mpg123 to pull in the stream off the net, feeds it as PCM to lame, which reencodes to the proper rates and sends it off to a FIFO, which is what icecast broadcasts.
So the problem I have now seems to be beyond my ability to fix. My icecast stream works great on this machine and on my wireless laptop played through xmms. But on sonos, it skips and stutters terribly. I know it's not a bandwidth issue, because the weak card on my laptop has no trouble with it. I notice that the sonos stream is slightly ahead of my laptop, from which I deduce that sonos is not doing very much buffering at all. And I suspect that's why it's stuttering. The stream works fine when xmms buffers 32K, so it must be less than that.
So, is there any hope? Do radio streams have to be absolutely perfect to work? I listened to Philly NPR for hours tonight with no problems whatsoever.
(Also, an aside: I know that the ZPs are perfectly capable of resampling streams that aren't 44.1kHz. Why don't they? That struck me as pretty weak.)