Thank you, all, for getting back so quickly and helpfully! I will definitely be contacting Music Hall to see if this is a fixed or variable line out (does anyone know why the former would be of any use to someone?). If it's variable, it'll be time to start sub shopping.
Also, I have a cheap Polk sub somewhere that I don't use. Maybe I'll test this output with it and see what happens.
Also, I have a cheap Polk sub somewhere that I don't use. Maybe I'll test this output with it and see what happens.