With regard to mapsonus sucking... does anyone know the quality of street atlas maps? They are probably better and if you look at the general procedure this guy is following:
http://www.vsa.cape.com/~danh/gps/
You can see that Street Atlas can export a route to file and that file format looks like basically the same thing mapsonus generates with regards to lat/long for each turn. So Street Atlas costs $50 and no one even has to reverse engineer the map data to use it.. well that sounds good eh?

I'd try this myself if I had my stupid Oncore unit working, I'm not much of a solderer...