Your graph sounds almost exactly like mine. I got a Behringer Feedback Killer and used it as an EQ and it worked a treat! Takes some tweaking and tricks, but it did a lot to flatten out my response.
So that's one way you can consider going...
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A Woofer in Tweeter's Clothing...
M60s, VP150, QS8s, EP350
Onkyo TX-SR702, Denon DVD-3910