Well, maybe I'm doing this all wrong, but I use the same 75hz signal for the sub that I use for the rest of the speakers. I get the control knob on the EP175 more or less in the ballpark, then make smaller adjustments with the sub's level control on the receiver. I think right now I'm +3db on the receiver's sub output. Everyone one of the speakers is +-3b of 0.

M22ti mains, EP175 sub, VP150 center, QS4 surrounds