Piping two inputs into comm

Question

I have two lists I produce using the following commands:

1. find . -type f -name config.php -exec ls {} \;
   

2. find . -type f -name config.php -exec grep --files-with-matches some_string {} \; | sort
   

How could I pipe the lists into com -23 so I can see those entries from list1 that aren't contained in list2?