PulseAudio
From D3xt3r01.tk
What
Start the daemon as the user you're going to play music/audio as.
pulseaudio -D
Get sinks list/indexes
pactl list short sinks
Set the volume to 100%
pactl set-sink-volume <index> 100%
More help/options:
pactl -h
You could use the GUI pavucontrol to set this stuff OR the cli stuff above.