Hi - our Promotions group replaced a MacPro with a new iMac. The old MacPro had a dedicated card that provided HDMI out to a client monitor. The editor used two monitors for their workspace. How does one specify the client monitor to get what is essentially "program out" while keeping the other two monitors dedicated for workflow i.e. browser on left and timeline, effects, timeline, inspector on the right.
In your preferences you can set your AV Output - set this to your client output monitor, then in the Window Menu you can select to turn on A/V Output. They'll see the viewer and the rest of the set up will be set up for your editor on their screens.