Walt Z. claims that Communicator does not play embedded audio, "particularly embedded QT audio Moovs with QT plug-in 1.1." Regular QT Moovs do play.
Michael Macrone adds: "Communicator will not load QuickTime MIDI files (and perhaps other types of auto-playing embedded content) unless the <EMBED> tag is located in the viewable screen area while the page is loading." If you wait until the page has finished loading, it will not work.
Update: A source at Netscape claims: "QT Audio files do indeed work with Communicator and the QT plugin 1.1." He is investigating the MIDI issue.