Speed is not supported in gpx 1.1. So there is in the Kurviger gpx 1.1 file for this its own extension added.
However the associated scheme (at the beginning of the file or anywhere where the extension is used) is not defined.
Garmin programs are very strict about file formats and refuse files that do not conform to the standard.
JaVaWa RTWtool is a little less strict and can read the Kurviger gpx 1.1 file.
Then convert it (= result without speed) to a gpx file, which BaseCamp or Mapsource can handle.