i use a
Blackmagic UltraStudio 4K for video playback (via Thunderbolt on a 2013 MacPro Trashcan). i feed the AES out of the Blackmagic into my MTRX and have it configured as a stereo source in DADman on my S6 MTM. i then have it configured as the default sound output in my Mac system preferences. works great, and works regardless of whether Pro Tools is open or not.
hope this helps.