The Sigma Datacenter software needs to be updated via their website for the export to .FIT and .GPX to function properly.
You have to go to the sigma shop for the datacenter site, create an account, then enter the CD license key that shipped with the unit.
Once I downloaded and installed the new version 3.2.1-005, the export works fine and imported into Strava with no drama.
First ride with the Rox - no cadence or HR or speed sensor data yet, just GPS
A side note on pairing the ANT+ sensors, took me about 20 seconds to set up the HR strap and the cadence sensor once I knew what to do. They very quickly registered to the unit.