A friend let me borrow his OmniMic2 Freq response test mic and software. I loaded it up and updated it.
Base graph with the mic sitting right about where my head would be in the sweet spot before any corrections.
Notice the left side (bass). I've reduced the hump at about 35hz by placing one carefully calibrated couch pillow at the back port. The dip at 77hz or so I softened by putting a pair of bass traps (2'x4' from ATS) at the inside of the speaker against the cabinet. This projects to the back and front of the cabinet. Front is even with the front of the speaker and the back is about 2" from the wall mounted bass traps. Doing this also softened some of the upper mid hills and valleys.
I tried putting damping on the top of the speaker - no measureable change.
I tried two pillows at the port - too much pillow.
I tried moving the bass traps around, they didn't do anything when placed to the outside of the speakers in any position.
I tried putting a blanket over the tv - it moved the graph around but it was not something I could hear.
I suspect the 590ish hz dip is crossover related. Nothing I did changed it in anyway at all.
Carefully calibrated couch pillows are now available for $2000.00 each not including tax and shipping.