It sounds like you want something like this:
http://www.consumer.philips.com/cons...CSHQNHKFSESI5P
It's crazy expensive, and I don't think there's a way for you to load up your iTunes music on it - I seriously doubt it's FairPlay compatible.
You'd get WAY more functionality and save money by getting one of these:
http://www.westerndigital.com/en/pro...sp?DriveID=243
And pairing it with a Roku Soundbridge:
http://www.rokulabs.com/products/soundbridge/index.php