Well, my last post met with a deafening silence, so I guess the rather long series of steps frightened everyone off!
If it did, I'm happy to report back with the 'Reader's Digest' version. The nice folks at the GPS Data Team forum have again stepped into the breach, and added another option specifically for Volvo owners to their toolset.
Now, you can go straight to
http://garmin.gps-data-team.com/extra/, import your file, either as a CSV file (my notes above on creating those still apply) or as a standard GPX file, then choose to save it as 'Volvo Route'. I have successfully tested a couple of files in my car. You can still run the XML validation check I described (step 14), but it shouldn't be necessary now. And that's it! You are ready to take a USB key and copy the file over, then import it into the car.
I will write up this simplified procedure in the feature I am preparing for Volvo Driver magazine, along with the creation of stored locations incorporating phone numbers you can call.
Cheers,
Julian.