This is the same system already used on the Colorado, Dakota, Oregon and the newest Nuvi models. Unfortunately, it isn't completely backward-compatible with mapsets created in mapsource that contain multiple products. So if you used mapsource to make a single gmapsupp.img file for your 60csx, that will not behave properly on any of these new units. You will only be able to turn all of the maps in that file on/off at the same time. You will not be able to select individual maps within the file.
The solution is to create new files which only contain one "product" each. But there may even be some glitches there with home-made maps. For example, if you use Sendmap20 to create a map file and name it NYtopo.img, then use Sendmap20 to create another file named TXtopo.img, these maps will have a generic name "Maps uploaded by Sendmap20" on the GPS. And the GPS will group them together, even though they are in separate files. So you cannot individually enable them on the GPS, they can only be globally enabled as a group.