The MMI box uses the OEM mic and supports Siri and Google Assistant either via voice keyword (‘Hey Siri’ / ‘Okay Google’) or by long-pressing the steering wheel voice button.
The MMI box essentially acts as an intermediary between your original head unit and display. While the box is inactive, the original video signal is passed through unchanged and your car works as before.
After activating the MMI box, the box’s video signal is shown on the display instead.
You can easily switch back and forth between the box and your original head unit. Using the MMI box is optional and should be seen as an add-on and not as a replacement.