If you want to be able to adjust the volume of your pc with a command line via Vixen and a launcher, it is possible by loading a command-line software of "nirsoft":

https://www.nirsoft.net/utils/sound_volume_view.html

this software is free.

first, you start the software and you find the name of your sound card (note, vixen sound only appears when vixen is started)
You must have this screen (the one is french, do not panic, the software is in native English):
soundvolumeview.jpg

in vixen display setup, , you have to create a launcher output:
setupdisplay.jpg

and this:
setupdisplay2.jpg

Now in the timeline, you have to create a launcher (1), then enter the path of the software (2) and finally fill in the volume parameter:
setupvixen.jpg

this trick allows you to adjust the volume of each part of your show and why adjust the volume in the middle of the Show .

Enjoy, see you soon.

(sorry for my english, i'm french)