I think there is a common format that allows some GPS mapping products to output waypoints and perhaps routes that can be input into the GPS, but if you're looking for something that would actually allow the 60CS to display the NG maps, I don't think that is possible these days with this or any GPS. AFAIK, each GPS is married to its own mfg's mapping products.
Garmin has a couple of Topo products.
I have the 60CS and like it a great deal.
If I'm wrong, I'm sure I'll get corrected quickly. Take care,