I just updated my MAC’s OS to Sierra 10.12.6 and my audio interface stopped working with Cubase 7.
Ive tried both a presonus and steinberg audio interface. Both do work with other signals from my comp (itunes, youtube) but not with Cubase after I switch the audio driver. All I get is a loud ringing sound.
Since you are using a non supported OS now, there will probably be not be much help, other than trying the “Steinberg Application Installer Tool for Mac OS X” which can be found on the Steinberg site, or using a version of Cubase compatible with your OS.