Count Check marks across columns

Hi I'm relatively new to SmartSheet and have a question.

I have a set where each row represents a requirement.  Each requirement may impact multiple systems.  Since I'm unable to select multiple entries with a drop down - I've created 4 column - each representing an impacting system.  I now need to summarize in a dashboard how many impacts each system has.  So for System A - x # of requirements impact it; System B - y # of requirements impact it.  How can I make that happen?  I tried creating a summary sheet and linking - I ran up against the 25,000 cell limit for links to external sheets.  I'm sure there is a better way.