Okay, after messing with the plugin a little more, I'm not sure if the option on Sources 2 is what we're looking for. It looks like it just enables certain taxonomies as individual search results. What we want is the ability to search for posts that are related to those taxonomies. This is similar to the taxonomy term selectors in Categories & Taxonomies under Frontend Search Settings, but we want the ability to select based on the search text input rather than having to select from a list. Is this possible?