For Airtunes, you can always get an Airport Express for under $100. It has both optical and analog outputs (on a combo 1/8" jack). Having this technology built into a preamp/processor or receiver would be neat, but not *that* much better integrated than a small external device connected to an optical input.

For what its worth, I don't believe that Apple has worked out the kinks in Airtunes enough to take this next step. I really love the idea, but their actual implementation leaves a lot to be desired. At least in my house.