A few years ago there was a tool called VMix Audio Controlled switcher which allowed switching of VMix inputs based on basic audio threshold settings. It worked pretty well and I used it in heaps of radio station installs.
It disappeared off the market and there hasn't been anything since.
As I used this sort of tool all the time, I decided to build a replacement. It builds on the basic capabilities of the original and adds some pretty awesome features such as direct support for ASIO interfaces, support for Dante and Support for NDI inputs. This makes it way easier to setup.

You can download a fully functioning trial from here: https:/w.np.co.nz/software