No idea, I don't use Mapsource at all with my 705, never have with any GPS.
I plot the route on bikehike.co.uk, download as gpxx, frig XML file by hand to name control/info location, and possibly split it into sections, copy gpx
Going back the other way I use GTC to receive the TCX history file. I also import the TCX files into GoldenCheetah so that it can do its magic with my power data.