The Mumble overlay does not work with Arma III, Civlization V, Takedown: Red Sabre and SWAT 4. Here is what I have already done:
I'm using the sound card of my Creative Tactica 3D Alpha Headset.
In SWAT 4 (non-steam) it is possible to get the overlay running, by letting the game load into the main menu and then start Mumble. DxDiag.txt included.