So I just read through the code of that plugin.
They’re using is_main_query() as a check before the plugin does anything, which is why it’s not working with WPSP.
On pages that have a WPSP list, the “main query” is the page itself, with the WPSP list being a secondary query. That’s why it’s working with regular posts, but not with WPSP.
I’m afraid I can’t really think of a way to make the two plugins work together. I am working on a filter functionality within WPSP Pro itself, but it’s not ready for testing yet.