Got it set up today. So far absolutely fantastic. My only problem is that when I'm playing via digital cable to my Theta DAC, it can lose sync with the Theta for a second at the beginning of a song and send static into the system. This may be due to the Theta not muting when losing digital signal, but I'm not sure. I do not think its a streaming or bandwidth issue, as my network is wired ethernet 100mb/sec.
There is no such issue when playing analog out from the Airport Express. And yes, the little Airport express processor is very good, (better than expected) but I still prefer the sound quality from the Theta Progeny A.