I solved this issue and the solution turned out to be super easy. I simply prefixed the absolute server path to the filename parameter in createDocxAndDownload() and set the second parameter to true.
I actually disovered this solution while reading the documentation page for createDocx(), where the filename pararmeter description says, "The path to the resulting Word document."
However, the filename parameter description for createDocxAndDownload() says, "File name of the document to download."
This might be obvious to some, but I mistook this to mean the filename only and led me to believe the path is defined elsewhere (like in phpdocxconfig.ini).
I would suggest changing the filename description on the createDocxAndDownload documentation page.
In any event, thanks again for the support. I'm happy to put this issue to rest.