My AP Express 1st gen could be selected fine as an Airplay device from iTunes. I installed SoundFlower and found that even though the Express was listed, I clicked and the selection would not stay. I.e. check box would appear then quickly disappear. I made sure that ipv4 was selected in network preferences as this can sometimes cause an issue. I also validated that I could play to the Airplay device from "Radium" on the same Mac (it's an internet radio player), using the Mac volume slider holding the option key and selecting AP device and my iPhone. I then installed SoundFlower using the uninstall Applescript in the .dmg and rebooted. Airport Express selection from iTunes works again. There most be some negative interaction bug in SoundFlower and iTunes.