I just bought a new iMac (late 2015) and migrated all apps from my prior computer. I also upgraded to Sierra.
Upon opening Roon I get the error message no audio devices found. My Meridian Explorer is connected via USB and is chosen in Audio Preferences. I do not see the DAC or my Airport express, which had been working as an endpoint before the machines were moved
here is a screenshot of my audio setup page in Roon.
Look forward to hearing from you