I have done this. The MTH remote will run legacy engines, but not in "Legacy" Mode. You lose some of the features of running Legacy with Cab2 remote or Cab3 app. I've never used a Cab1, but I assume, it would be more like the functionality of a Cab1/TMCC.
In the DCS App, at the bottom of the engine list, where you add a DCS engine, there is a line that says "Add a Legacy/TMCC engine".
You have to click on that. Of course after you have everything wired up with the Ser2 etc.
Mike