There is something unique about the ESPN Radio stream (http://opml.radiotime.com/StationPlaylist.axd?stationId=25876) that prevents it from syncing.  If I start the stream on sync'd players, it will occasionally play in sync, but most of the time the players will be out of sync by at least a few seconds.  Sometimes (but usually not) I can get them to sync by turning one of the players off/on or unsyncing/resyncing, but none of these tricks are reproducible.  I have no problems with syncing any other internet streams or other music sources.

(I haven't had time to test this with new-streaming yet...)