I see where you were coming from, but as stated already, mdma wont necessarily mitigate the anxiety.
In fact, i would think heavy doses of benzos would have little effect on whether you get anxiety or or other unpleasant feelings from dmt.
The launch is so quick, you wont have time to think so anxiety isnt really anxiety.
At least with dmt or salvia etc.
However, pre launch nerves, yes, medication may help if this is reallly so required. But i would question whether taking the planned drug was worth it at all if this was the case.