KMZ is the GE zip file format. Use KML as your Save As File type from GE. Download and install GPSBabel ( GPSBabel link (http://www.gpsbabel.org/download.htm) ). Your input format will be KML and your output format will be GPX. You should end up with your path being a track with the same name you used for your path in GE. You can can also set a filter in GPSBabel to convert the track to a route. (There is a limit of the number of waypoints you can have in a route though.) Humminbird PC will complain about not finding the declaration of element 'gpx' in the GPX file, but it can open the file. Then you can copy the track / route to another file or upload it from there to your unit.
Click to enlarge => (http://photos.imageevent.com/limbatus/2010/misc1/small/GPSBabel.jpg) (http://photos.imageevent.com/limbatus/2010/misc1/GPSBabel.jpg)