A new installer (v2.1.6c) has been posted that addresses a previously-reported issue with freshly installing Media 100 Suite v2.1.6 under Mac OS X 10.11:
Download Media 100 Suite v2.1.6c
Boris FX has not yet qualified Media 100 Suite for Mac OS X 10.11. Media 100 Suite v2.1.6 should be considered "beta" software for this new Mac OS. For those who are willing to try v2.1.6 with El Capitan, please report feedback on the Media 100 Facebook Group or at Creative COW. When testing beta software, we strongly recommend setting up a test system, and not installing the software on a system you are counting on production.