Output sound can't be changed
Try this alternate way to control volume from the terminal:

sudo osascript -e "set Volume 5"


Change the "5" higher or lower to make the volume go up and down in intensity.
This will put your volume at pretty much the lowest setting above 0.

sudo osascript -e "set Volume 0.25"


the highest I believe:

sudo osascript -e "set Volume 7"