Recently I've been trying to execute on the vision of streaming audio from my iTunes/iMac store to my home stereo.
It's been surprisingly difficult. The iTunes/AirPort/TuneConnect combo sort of works (thanks to TuneConnect, no thanks to Apple). The non-Apple solutions from Sonos, Roku and SlimDevices all seem less than they should be.
Why is that? The technical challenges seem to be manageable. The answer, I fear, is Digital Rights Management (DRM) and, indirectly, the foul and insufficiently feared Digital Millenium Copyright Act (DMCA). In this case the DRM is Apple's FairPlay (not their AAC file format, rather the FairPlay DRM controls), but the flavor of DRM isn't relevant.
We want to be able to stream compressed music (bandwidth!) from a server to multiple synchronized or independent receiving devices. The receiving devices need to be able to communicate with the server and have their own volume and on/off controls. The receiving devices need to work with a remote control and they should display playlists and the like (those could also go on the remote). The receiving device should be compact, quiet, and cost under $200.
All of these things are attainable, but for the unanticipated side-effects of DRM. This is tricky, but follow the logic chain. Apple can't do anything in their software or hardware to make the Apple Store DRMd music experience inferior to the 'rip a cd' experience. This means if they implement a solution that allows one to stream bandwidth efficient compressed music to a music player, the music player must support Apple's DRM (FairPlay).
Ok, that's maybe doable (though in fact nothing but a PC or Mac currently supports FairPlay -- so maybe it's not so easy to do). Imagine the device supports FairPlay. Now someone breaks FairPlay. Fine -- Apple patches their software to force one to update the DRM mechanism. Problem is apple has no direct control over the FairPlay implementation in the peripheral device. So they either break the peripheral (can't play the new DRM implementation), or they can't fix their hacked DRM.
So in order to protect their DRM, and keep their partners happy, Apple can't stream DRM'd AAC music. So they can't stream any AAC music. So they can't do network efficient music streaming to non-computer peripherals, and they therefore can't stream to more than one Airport Express (or any other device) at a time.
Perverse and very bad consequences. We haven't even begun to explore all the nasty side-effects of 'digital rights management'.
see also: Apple's foray
Update 11/9/05: This patent is probably relevant to this issue.