This is because audio|acacia does not yet know what type of AirPlay device it is, so a generic speaker is shown instead.
-For official 3rd-Party AirPlay devices that show as a generic speaker, please submit a bug report.
-For unofficial 3rd-party AirPlay devices (i.e. XBMC, Shairport, etc.) a generic speaker icon will always be shown since these are not officially supported nor recommended.