Certainly maps cannot be shared between 2 units. The favourites, etc. are stored in the mapsettings.cfg file located in the specific map folder. I have my doubts that even this can be shared, even if the map is the same on both. You can try it but make sure you've made a nExplorer, not Home, backup first.
What many people do is convert the favourites to a custom poi category. Download poi edit from poiedit.com and input YOUR mapsettings.cfg file. All your favs will appear. Save each item as a point in a custom poi category called, say, '_My Favorites' (no quotes). The _ at the beginning ensures this category will 'float' to the top in your poi category listings.
This custom poi file will get saved as a .ov2 file and you CAN then not only copy it to your map folder but also to the map folder on another unit.
Whenever you get a map update for a unit, just copy this ov2 file along with all your other ov2 custom files to the new map.
By the way, make sure you register the new unit at TomTom using a different email address (doesn't even have to be a real one) than for the first unit.