Currently there is no way to add an application without it being recognized in the Windows Volume Mixer, so you have to open the program and play audio out of it to add it to a group.
It would improve the experience greatly if there was a way to add custom .exe files or a scanned folder that MM could latch into when they are started.
Example use case for folders:
I used to have Spotify installed through the Microsoft store, and each update it would change the name of the exe, such as Spotify[version-number].exe, and MM would require that I re-add the new exe and delete the old one on every update. If I could add the folder where Spotify was installed, this would not be required; MM could scan the folder automatically, and add the exe to the group.
Example use case for .exes:
Also, sometimes I want to have multiple programs on one group that aren't in the same place (think like Ableton, Resolve, Resolume, Atomix VirtualDJ). Basically a group that controls all creative software. The way to do this right now would be to open each program independently, play some sort of audio, then add to the group. If custom .exes could be selected, it would be much simpler; choose to add a custom path, navigate to desired .exe, click add. Then when audio is detected from said program, MM could latch onto the volume.