The newest version of GE (3.1.1.0) as of March 27, 2014 is still not compatible with the Montana 600.
GE still indicates that an update is available, runs the update process, and reports that the update is complete. It also continues to report that the very same update is still available. So I run it over and over and over and over, and it continues to indicate successful completion and that the same update is available.
So it looks like GE is still not ready for the Montana.
A late model 2013 MacBookPro Retina running Mavericks (the latest) and a Montana 600 running the latest firmware, CN lifetime update, and Garmin TOPO maps are in play here.