If you are interested in a comparison between Roku and Apple TV, I'm sure there are several articles out there in internet-land to read. Here's one for instance:http://blog.streamingmedia.com/the_b...he-winner.html
You mentioned iTunes (audio) -- the Roku can interface directly with the audio files in your iTunes library using a "Private" channel that is available. I can give more specifics if you're interested, just know that it's possible. Although, audio support for the Roku in general is primarily limited to mp3.
I own two Roku boxes - one of the newer XDS models and one of the original HD models. They are great little internet streamers (Netflix, Amazon VOD, etc.), but aren't really suited for playing content off your local network. You can do it, but supported file containers and codecs are severely limited (primarily mp4 and h.264), and the overall experience is not really very user-friendly, especially since it requires a server to serve up your content instead of being uPnP/DLNA compliant or being able to access SMB shares. So, if playing back local content is important to you, I'd suggest using some other STB, since there are several out there to choose from that do it much better and easier than Roku.
One of the main differences between the new Roku boxes and the AppleTV is that the Roku supports 1080p, while the AppleTV does not. HD content is primarily available from Netflix and Amazon VOD, although not in full 1080p at the moment. Netflix has said in the past they plan on providing 1080p at some point in the future.
There are a few live-streaming sports channels available on the Roku, including MLB.TV and I believe NHL Gamecenter is slated to come to the box very soon.