I need to determine overlap between two multi select text fields

I don't have a good understanding of what your tables or workflow is. In your description you mention (1) Procedures, (2) Requirements, (3) Audits and (4) table to table imports. Which of these are tables and what tables are involved in the potential table to table import? Also in which table is the multi-select field and what options does it take?

I would just describe your existing table and field structure without regard to what the final solution might be or if it can even be done using native features. I am 100% confident this can be solved using script and you will probably be amazed at how short the solution is. But I really don't understand how your application is structured.