An update.
I followed info on another topic that suggested:
- Putting the .jar files in 'C:\Users\[username]\AppData\Roaming\Stencyl\stencylworks\extensions', and
- Putting the folders resulting from extracting files from archives to 'C:\Program Files/Stencyl/Engine-Extensions'
Including a note on this may be a good idea.
It seems to be working but have to try it out in the next days. Thank you again.