In June, I wrote about how AirTunes works, based on a briefing I had with Apple VP Greg Joswiak. At that time, I reported a fascinating feature that Joswiak mentioned to me:
If iTunes is playing back a digital multichannel file format like AC3 (Dolby Digital) or DTS, those bitstreams are wrapped in Apple's compression and encryption, and then decoded at the other end. In those cases, AirPort Express would end up streaming the raw AC3 or DTS stream via an optical cable to your home theater receiver for decoding.
Here's the thing, though: for the life of me I couldn't figure out how to get an AC3 or DTS file to play through iTunes. Dropping those files into iTunes has no effect. It just doesn't work.
Then, this weekend, I discovered Apple Knowledge Base article #93870, Playing DTS audio files with iTunes. It says, in part:
iTunes can play DTS (Digital Theater Systems) encoded audio files through the optical audio out port on an AirPort Express Base Station connected to an amplifier (or powered speaker set) with a DTS decoder.
The problem is, Apple still doesn't actually say how you'd actually get that file into iTunes. And I still can't get it to work.
I get the sneaking suspicion that iTunes 4.6 doesn't actually support these features, and that we're all waiting for the other shoe to drop. Unless someone out there can tell me how to add a DTS file into iTunes, that is.