Color managed project and external video device

Given that mercury transmit seems to circumnavigate the Display Color Space drop-down when in a color-managed project and sends a very wrong-looking image to my Blackmagic Decklink, what is the workaround if there is one? It's impossible to run a client session like this and plus, I miss my external monitor.

Who needs to fix this, Adobe or Blackmagic? Surely Adobe needs to make Mercury Transmit follow the same output transform as the composition viewer or are video device vendors expected to build OCIO transforms such ACEScg>Rec709 as an option in their software?