Thanks for your reply. The room is mostly symmetrical and the speakers are similarly placed in terms of distance from the walls. I do have 4 inch absorbers at the first reflection. It might not be perfectly placed.
My subwoofers are 21 inches each in huge 3 x 3 x 3 ported boxes. I forget the model numbers but they should be pretty potent. I will look at my equalization settings and see what’s going on there.
When you say first reflection point, do you mean when the sound from the speaker strikes the opposing wall or behind the speaker and the wall it is near?
The technique I am talking about puts the speakers extremely close to the walls, with only enough distance to sandwich an absorber between.
http://arqen.com/wp-content/gallery/room-setup-speaker-placement/speaker-placed-close-to-wall.jpg - Taken from this article
Diagnosing that 200Hz dip might be simple. 200Hz wavelength is 1.71 metres, so the cancellation is likely caused by a boundary/object which is located approximately .85 metres from the woofer of said speaker.
Subwoofers that size should definitely play below 40Hz, unless they are PA subs with a high port tune. Although I assume that isn't the case.