sndio.el is a major mode to interact with sndio(8).

sndio.el screencast

Activate it with M-x sndio RET, then the following bindings will be available:

d sndio-decrease
g sndio-update
i sndio-increase
m sndio-mute
t sndio-toggle
n forward-line
p previous-line

or call M-x sndio-win-open RET to open a popup window to quickly change the volume and then q to quit.