1) Open ‘Activity Monitor’ app on Mac
2) Kill any ‘Native Instruments’ applications/processes running (I think mine was Native Access but not sure now can’t remember)
3) Kill the ‘Audio MIDI Setup.app’ program/process.
4) try install the firmware update now (if the installer isn’t registering anything (ie. it says ‘No Device Connected’), then take the USB cable out of the Mac & plug back in immediately, this should detect the correct update to install. If the ‘Start Update’ button is greyed out then take the USB cable out & plug back in AGAIN and it should become available.
Hope this helps the several people in this forum I’ve noticed who gave up/ might not have resolved this problem still.