I do not know anything about the 'modern' garmins or the 64s.
I have a 60, 60Cx & a 60CSx, to load maps onto the Cx & CSx I have to first install them into the Garmin PC program Mapsource, then plug in the GPS & install to it from Mapsource.
The other option is to buy a SD (or is it a microSD) card with maps pre-loaded.
I use the OzTopo map which is the very best whole of Australia map on the Market.
yacht racing at RMYS
Lake Mountain Ski Patrol
bush walking anywhere in Vic