When it tried mumble i had a massive echo + loop problem , when i tried to set up the ausio in the wizard it already repeated what i said several times , sometimes it didnt stop untill i restarted mumble. same for people talking to me .
The solution to this , after i updated the drivers, Directx ... was that i just enabled Full HRTF in teh direct sound options. I dont know why but it made the problem completely vanish.
So if you have a connexant AMC Audio device ( cant get more info about it anywhere :/ ) try setting ( in expert mode) the HRTF to full.