An update on solving the Concurrent Conversion issue.
The 'homeFolder' example made absolutly no difference.
After trying a variety of ideas, I was finally able to get the 'UserInstallation' exaple to work. This required removing the existing 'UserInstallation' definition in the phpdocxconfig.ini file.
The 'UserInstallation' definition supplied via code does not overwrite the 'UserInstallation' definition in the phpdocxconfig.ini file even though the 'UserInstallation' definition supplied in the code appears in the command passed to the .exe (it appears after the definition from the phpdocxconfig.ini file).