In one case, having the 002 or 003 selected in the Audio Devices window of AudioMIDI Setup selected was preventing Avid CoreAudio Manager from launching. This stopped the 002/003 from playing iTunes (and web browser sounds) even if the 002/003 was selected in System Preferences > Sound. Select anything other than Avid/Digidesign hardware in AMS’ “Audio Devices” window. It is not necessary.
Also, be sure to download and installed the latest Avid firewire audio drivers from www.avid.com