Found the bass culprit in my monitor speakers...

I'm sure. My father's B302a speakers were a glorious part of my childhood. With a Dynaco stereo they would play 95 db or so beautifully.
He had an Ampex real to reel and the prerecorded tapes he had were incredible, a lot of Jazz and classical. I miss the hiss:)
What a dummy I am. I spoke to an old friend of mine who was into Bozaks. The insulation was to kill resonance between 500 and 600 Hz, the wavelength of the inside of these large enclosures! I should have thought of that. 
Millercarbon, I'm afraid it does not quite work that way accept at certain frequencies that keep ringing after the cone stops as in the Bozak example above. Inside the enclosure sound waves are pressure waves that at low frequencies help determine how the cone moves. Sound from the midrange driver which is open in back in the Bozak does not leak out through the woofer cone. The woofer cone is too stiff and heavy for that. Very high frequencies might but in this case the tweeters are mounted on a bracket out in front of the woofer. At low frequencies the whole cone moves influencing it's frequency response. The enclosure vibrating is a problem and is a form of distortion. In the B302a Bozak this created the very warm bass that a lot of people like my father loved. That enclosure was a musical instrument! It was just 3/4" plywood without any bracing. Nobody would make a speaker like that today. But in that Bozak it was euphoric as hell. 
Now I am all for Room Control which is actually speaker control. Most people use it in subwoofers only and downplay it for full range use. I use it to equalize the satellites so that they have absolutely identical frequency response curves right out to 20 kHz. The result is pristine imaging. No two identical drivers are exactly the same and no two drivers occupy the exact same place in space. Two identical speakers in two different locations sound different to various degrees. We locate sound sources by differences in volume and phase (arrival times between ears.)
So, if you want a voice to image dead center the sound of that voice has to arrive at both ears at exactly he same time at exactly the same volume. If the volume of various frequencies contained in the voice is louder in one speaker than the other you essentially dissect the voice and spread it out. The image becomes bloated. Most people try to control this with room treatments. It is much more accurate to use digital speaker control where you are actually measuring the exact frequency response of each individual loudspeaker and correcting them so they are exactly the same. Works great:)

stereo5, yes you are right. My father had a pair of B302as and as you describe they had I think it was fiberglass insulation probably between 1/2 to 1" thick stapled to the inside wall of the cabinet. They were doing that I think to reduce resonance in the enclosure walls although I can't see how that would work. It would not in any way work in the same way acoustic cotton works in a smaller sealed enclosure. To work the cotton has to just fill the entire cavity. Also in a larger enclosure the pressure (temperature) changes are not as extreme so even if you filled the entire cavity the effect on the systems resonant frequency would be negligible or greatly reduced. The point being that it is not acoustic stuffing in the usual sense, it is dampening of some sort. Maybe there is an old Bozak designer around that could fill us in:)

Mike

The original paper on this was done by Acoustic Research in I think it was 1954. They released the first "acoustic suspension" loudspeaker shortly there after the AR-1. Before then most speakers were infinite baffle and much larger like Bozak speakers of the time which did not use any stuffing. 
bdp24 the air molecules "moving around" does not explain the increase in enclosure size perceived by the woofer . As I explained above it is a thermal-barometric principle.
Obviously, a speaker can be over filled which happens as soon as you start compressing the acoustic cotton. It has to just fill the enclosurewithout compressing it. 
I think "monkey see monkey do" insults the intelligence of many thoughtful speaker designers out there. An excellent manual on the subject is The Loudspeaker Handbook by John Eargle. 
Audiodav if you like the sound better than let the force be with you:)

Audiodav unfortunately not a good idea. The acoustic filling in speakers essentially makes the enclosure seem about 30% larger to the woofer than it actually is lowering the system resonance frequency and improving low bass frequency response. It is a bit hard to explain but it does this by making the system more isothermal. When air is compressed it heats up further increasing pressure. The opposite is true under vacuum. The stuffing absorbs this heat on the compression stroke and releases it under vacuum stabilizing the temperature inside the enclosure making the enclosure function as if it were larger. What you have done is decrease the low end reach of your speaker and raised the resonance frequency which is going to increase the volume of the midbass which is what you are hearing.

Mike