Bind this to your media keys to control whatever pulse audio syncs are active.

volume.fish

#!/usr/bin/env fish

set -l current_sinks (pactl list short sinks | grep -i "running" | awk "{ print \$1 }")

for sink in $current_sinks
    switch $argv[1]
        case mute unmute
            echo "toggling mute"
            pactl set-sink-mute $sink toggle
        case up
            echo "volume up"
            pactl set-sink-volume $sink +4%
        case down
            echo "volume down"
            pactl set-sink-volume $sink -4%
    end
end