Make sure the Thunderbolt cable from the Blackmagic Intensity to the Computer is connected
This is the Blackmagic device that delivers audio and video to the Plasma Monitor you can't see this because it is in the A/V rack hidden FYI
Turn on the Plasma using the Remote – Make sure it is set to HDMI
Go to your System Prefs
Select Sound
Select Output Tab > Blackmagic Audio
Select the application that you want to run
Audio will be routed out the headphones and Video will be on the HD monitor.