What I'm saying is, the hump on your graph from 100-150Hz looks like the dark blue line on my graph. If you manually change the distance in the receiver and re-run the sweep, you may find that you can bring that hump down. That hump makes the other bass frequencies sound less powerful in comparison. To take all of those measurements in the graph above, I just changed the distance setting between 3'6" and 8' at 1~2 foot intervals.
My sub is right behind my couch, and I think with the phase setting at 180 on the sub, 3'6" or so worked best. With phase set to 0 on the sub, a 6 foot setting gave me the smoothest response.
If it werent for the fact that my subs are playing from 100Hz and lower, and my Mains are playing from 40-60Hz and upward your argument would be true
Also, I think you might not understand what the crossover settings in the receiver are doing.
Unless you have changed your settings since you posted it, this is what you have:
Mains : 40hz
Sub LPF: 100hz
Basically, the sub plays A) the .1 LFE signal, which can go up to 120Hz, and B) re-routed bass from the other channels. You could have bass down to <20Hz play through the front three speakers and the LFE in an explosion, and you want all of that massive bass energy to be played by the most capable components, the sub(s).
I suggest you up your LPF for the sub to 120Hz.
And wherever the crossover for the other speakers is set to, it sends bass below that to the sub (at a slope to mix the output of the sub and the speakers). So if there is an explosion, and bass goes to the LFE channel, plus left + center + right, the sub is playing the LFE channel and the speakers are reproducing most of the bass because they are crossed at 40~50Hz. The sub should be playing that mid-bass, and it's not if you really have those xo settings right now.
If you still have the crossovers set to 40~60Hz, I suggest you up these to 80Hz and see how that sounds. No matter how flat your graph is at 80dB, your subs will play the 40-80Hz content from the speaker channels with much more authority and power than your speakers ever could, especially with peaks at 90-110dB. I think this is what you're missing. Your massive subs will play 40-80Hz with much more authority than the mains. That should bring back that chest thump you are missing.Just change the crossover for all of your speakers to 80Hz in the receiver and see if that gives you what you're missing.
Even if you got 1 or 2 MBMs, if you were to run them off of the subwoofer output on the receiver, you'd have the same exact problem. I think your subwoofers are currently only playing LFE + sub-40Hz bass from the mains. The MBMs play 50Hz up to about 120Hz~150Hz. If you don't change your speaker crossover settings, even with MBMs your speakers would be playing all of that mid-bass in the 40-100Hz range (except for the LFE channel), and you would have the same exact problem.
One more thing to check... Do you have any crossovers on your subwoofers engaged? Any Low Pass Filters? If you do have any crossovers engaged on your subs, you are filtering out a lot of bass and a lot of SPL. Turn them off.
As an example, here is my subwoofer without the mains. But it's running through the left+right channels so the receiver's 70Hz crossover slope for the subwoofer is tapering off the bass above 70Hz. The red line is what it's supposed to be. The blue line is what happens to that bass when I turn on the sub's internal crossover at the max 90Hz setting. You can see how much bass energy it cuts out from the re-routed bass (basically double-filtering the bass), not to mention what that does to the bass in the LFE channel that can go up to 120Hz. Everything between the two lines would be the missing bass volume.Lesson: Turn off or bypass any crossovers in your subwoofers.