If you use Mapsource, WinGDB3 is an essential extra tool, IMO. Adds loads of stuff that should be in Mapsource but isn't.
So, in summary, that workflow for combining Route and Track is:
Plot a route in Mapsource, using autorouting, only placing 3 waypoints.
Save as a GDB file.
Run WinGDB3, choose option 11, "convert routes to tracks with all route points"
Then open the generated file in Mapsource, it now contains a track with 588 trackpoints, which follows the original Mapsource route.
(Following the above, you will now automatically have two instances of Mapsource open, one showing the Route and the other the matching Track).
Select the Track (highlight) and copy it.
Move to the other instance of Mapsource and Paste.
Select the Track and in Properties, name it, colour it green and downsample it to <=500 points.
Save the combined file, and transfer it to the GPS.
In the GPS, if it supports Routeing colour, set the colour to white (or yellow, which makes the route mostly 'invisible'). Of the Etrexes, only the HCx models can do this, on the others you're stuck with magenta. (New versions of Mapsource also support Route colouring, but it doesn't transfer to the GPS)
Check the Track is set to 'show on map'. Select the Route and choose 'Navigate'.
Some screenshots here