I don't understand how you've currently connected the H9 to your mixer, but it sounds like you have it attached the main outputs of your mixer?
Have you tried connecting it to one of your mixer's aux sends? Then you can send particular channels to the H9. Hooking things up this way will only work though with certain kinds of effects like delays and reverbs. Using the H9 as an aux send will cause phase cancellation problems with other kinds of effects like modulation.
