Command line per-application volume (maybe amixer or pactl?)

I can change the master volume with these commands (from the command line), and it affects all applications, but how do I change the volume for just one application (XMMS for example)? amixer -q set Master toggle # or pactl set-sink-mute 0 toggle amixer -q sset Master 5%+ unmute # or pactl set-sink-volume 0 -- -5% amixer -q sset Master 5%- unmute # or pactl set-sink-volume 0 -- +5% pacmd dump # is interesting, and there are GUI applications that can do this: gnome-control-center sound, pavucontrol