http://www.slimdevices.com/

The SqueezeCenter (formerly SlimServer) server software runs wherever the music library resides, and can access iTunes data, although I don’t use it that way so I’m not sure how complete that integration is — I let it build its own database of music, and run it on Linux anyhow. But here’s the iTunes integration page on the wiki:

http://wiki.slimdevices.com/index.cgi?BeginnersGuideToiTunes

The device itself is a plain old audio component, with the display either on the device itself (on the Squeezebox, a very bright fluorescent display) or the remote (for the Squeezebox Duet, a color touchscreen on the remote). The Squeezebox itself connects over wifi, and even supports WPA2.

The server software’s open-source and extensible, and there’s a decent library of community-provided plugins, that do everything from easy access to BBC or Live Music Archive streams, to displaying phone caller ID on the SqueezeBox’s display. Mine even gives me a weather forecast when it’s turned off.

http://wiki.slimdevices.com/index.cgi?SlimServerPlugins

I’m not 100% sure it’s what you’re wishing for here, but it’s a great way to get local and network music to places where a little piece of hardware fits in better than a computer. The audio signal chain is excellent, too, with a great onboard DAC. I’ve ripped my own collection to FLAC, and our Squeezebox is basically the only way we’ve listened to music at home for the last few years.