I'm just catching up on this thread, but have a couple of comments.
For that null in the 90-110 Hz range, I would look to your M22s as they are contributing most of the sound in this range. Try playing with their positioning if you can.
For bass traps to be effective, you need them as thick as possible and you need as many as possible. For the corners I would go with 6" thick minimum, and would fill the corner solid as Chris suggested if you can. Make sure the stuff you use is a minumum of 3lb/cu.ft. in density or its useless for LF.
You need to fill all 4 corners at a minimum, and if you can, also treat wall/floor and wall ceiling intarfaces as well.
You might be better served to spend the money on a second sub. From reading about others here that have done this, it goes a long way in smoothing out the frequency response.
"Unfortunately" I have the in/on wall version of the 22's, so I can't move them. I can physically feel them putting out decent bass when the sub is off, so I think I probably just had the sub too high in level when I performed the test at that higher frequency, which I only did once. I was just charting the graph so volume wasn't really important, so I didn't bother to change it when I moved the sub around. I had the LPF set at 90 hz, so it makes sense to me.
After easing my mind of this for a few hours tonight and watching the hockey game, I think I do (and my wife, surprisingly) agree with you in that the next step should probably be a second sub. Why spend even a few hundred bucks and hours of my time on some traps which don't look too hot, when I can put that towards a second sub which will help more anyway? I think I'll do the traps after that, and first reflection panels. I think those things look cool... Kind of hardcore
