For the fun of it, try these links and play with the URL:

For extra
For standard

If you looked at the URLs of the two available, there's:

http://server.conitec.net/gsa6p/key.exe for professional
http://server.conitec.net/gsa6c/key.exe for commercial

Note the gsa6p and gsa6c. Since the last letter changes and is the first letter of the edition, logic would say that your best bet would be to use e for extra and s for standard. This only works if the file actually exists or you just get a 404 error.