I've had the very same problem. Recently I have moved from a 2008 Mac Pro to a 12 core 2010 Mac Pro and could not get Mac to operate with my StudioLive 16.4.2 (classic) properly using macOS Sierra. When I started my Mac with a cloned disc from my "old" Mac, I realized that my "new" Mac was still not working properly running Mac OS X 10.6.8, which previously was not a problem at all. I suspected that there would either be a problem with the Firewire bus 800 to 400 connection, and to verify that the StudioLive did not have any internal issues, I reconnected to to my old Mac.
Running my old Mac with MacOS X 10.6.8 as well as Mac OS X 10.11.x connected to the StudioLive without any problems.
Hence I concluded that there must be a problem with my new Mac. I followed the troubleshooting guide which I had found on the Knowledge Base. I uninstalled the Universal Controller, deleted any "left over files" manually, shut the Mac down, started it again, ran First Aid (in the Disk Utility app), restarted the Mac and reinstalled the Universal Controller (v. 1.7.4).
But it was not until I restarted the Mac yet again, and deleted the PRAM that the StudioLive would work properly again.
Maybe this would work for you as well. Give it a shot.
Hope this helps,