Underflow simply tells the user that not enough data is being sent for AUNetReceive to process. Almost always, if you see this, the issue lies beyond Spectre.

Tips:


Be sure you disable any applications or utilities that may interfere with your network.


If you're on a network (wireless or otherwise), completey disconnect your machine from the network and see if the issue persists. 


Users have had success after removing their System Configuration folder:

    /Library/Preferences/SystemConfiguration

Note: This is your System Library, not your User Library.