Just curious, how far from the front wall are your speakers and from the back wall is your listening position? If moving the speakers front/back or side/side didn't do much, then it's likely a floor/ceiling mode not a wall mode, or possibly a combo of the two. Tricky to solve, but not impossible. Between some more positioning tweaks, some carefully selected and placed room treatments and utilizing the peq feature on the subs, you'll tame that beast pretty easily. Also if there is a door in/out of that room (not sure if it's a spare bedroom or a living room) then try leaving it open. My room is a small spare bedroom that has a nasty 45hz spike when all closed up, but if I leave the door open that spike is nonexistent. Food for thought.
-Lloyd