All right, I think I found a place to do "Export" in StreetAtlas 2K3, it's the only place I could find it. The problem is that it exports what they call the "Draw Layer". And by default, there's nothing on the draw layer. You can copy stuff from your map to the draw layer, for instance, you can select a segment of your planned route and copy it to the draw layer. But you have to do it one segment at a time. I can't see how to export the entire route in one step.

Arg, this is frustrating. StreetAtlas 2K3 is a nifty program, and it looks like it does oodles better than MapsOnUs in terms of accuracy, so if I could get it working with GPSapp, I'd be a happy boy.