I believe you cannot make this work without modifying the relevant engine code to enable async processing of the voice. This will likely be updated in the future that will enable the feature for you, so i guess you can either just wait and go without the voip feature for the moment, or modify the engine code, or create your own voip component that have the setup required for async proc. Afaik the new Audio Mixer is only an experimental feature so far, don’t expect everything works as smooth 