On most, there is a drop down box where you can choose caliber and thread. For instance the Sumo has one for the FX threads (and that's not an adapter, or at least not an extra one). They should be the shroud threads. M20x1 I think.
The alternative is remove the shroud and thread it to the liner retainer which just happens to be 1/2-20 UNF. It will reduce the weight and is just as stiff.
That's what I thought the drop down menu was for. But the shroud and the Donny endcap are both female. I guess I misunderstood the drop down menu, as I assumed choosing the FX/22 option would have it arrive ready to screw on or at least with the needed adaptor. Live and learn I guess.