I don't have any answers for you (I'm considering getting one actually) but could you tell me if the optical out can passthru 5.1/DTS from a macbook?
I must admit I don't know off-hand, but after a google, it looks like it's been flaky on previous AE models:
http://www.avsforum.com/t/1363174/dts-wavs-no-longer-working-with-my-airport-express
Seems like they don't test it when they release new firmware :S