Scott, the Sb121a needs a line out or power amp out signal. I tried using the monitor out on my Mackie 808S and didn't get enough signal. I don't know if a headphone out has enough power in it either. Check out your set up and see where you have a line out out signal. As I told you in a previous thread, the EV sub is light and powerful - I'm sure you would like it. Too bad you're not near me, I'd let you use mine for a job or three.