line in for itunes - Use computer audio in or 3rd party device

I wanted to know if there were any devices or a way to get something recognized by itunes that you could plug in something like a live band, that would be recognized as a device and then just select that device and it would play the audio from that thru itunes.

The reason for this is I use apple remote and airport expresses throughout my house to play music. It would be nice to be able to pipe in sound from another source and select it thru apple remote and play that audio thru the airportexpresses.

For example, someone brings over a record player and we hook it up, plug the RCA outputs into the device or line in on the computer. Then when itunes is opened the device/line in shows up as a source, and I guess to fit into apples schema, there would be one "song" on the device and it would just "play" that which would then send the incoming sound thru itunes and play over the speakers thru airportexpress.

Im suprised there is no device or option to play "line-in" or maybe there is a way to have the sound line in of the computer be used. Im sure there are lots of applications for this. I suppose its possible apple doenst want this option but maybe someone out there has some kind of work around to accomplish my goal.

Thanks

james

Maybe it could be something line a live podcast or personal radio station that could be set up. I just thought of this looking at the catagories.