How to use Pigz with Tar
Mark Adler's top voted answer on the SO link that you included in your question does provide a solution for specifying compression-level as well as number of processors to use:
tar cf - paths-to-archive | pigz -9 -p 32 > archive.tar.gz
To pass arguments to pigz using -I or --use-compress-program, you can enclose the command and arguments in quotes, like so:
tar --use-compress-program="pigz --best --recursive" -cf archive.tar.gz YourDataHere's a fun option to monitor the speed of the archive creation:
tar --use-compress-program="pigz --best --recursive | pv" -cf archive.tar.gz YourData