I'm the user from the mentioned thread - here a bit more details. I had this same problem - try redownloading the installer from your purchase receipt email. Right-click on the installer file (FSDT_Universal_Installer.exe), select "Properties", then click the "Details" tab. The latest version should be 1.0.66. If not you have an older version of the installer, in which case there may be an issue with the link in the email. I uninstalled the old installer, ran the new .exe and GSX Pro then showed up in the list.