To change the audio volume from remote of my Mac at home, I needed a command line tool which I can use via ssh. I've found it here: OS X Daily - Change the system volume from the command line. It's as easy as
sudo osascript -e "set Volume 10"
You can enter numbers from 0 (mute) to 10 (maximum).
How to play an audio file from command line is described here: macosxhints - Use a built-in command line audio player. You just enter
More information on how to use afplay is available via afplay -h.