Assuming you are running everything in mono, there isn't really a "second output." If only one cable is in the H9 output jacks it will mix the stereo effect output to mono.
You could do as you say, and connect a cable to the second output, but this means you will only get half the stereo in your effects loops and the other half to your console.
But that may work for you. Otherwise, you probably should use suitable Y-leads or DI-boxes instead.