Box Too Big

Alright.  Check this out:   http://www.bcae1.com/xovrslop.htm

See how the slope gets much steeper at 24db?  Your friend's system looks like the crossover point there.  Only the points don't match up - one is at 80hz and the other is at 125hz.  And his situation is even worse - because his subwoofers are probably "hot" (more efficient) relative to the midbass drivers under 200hz.

Just adjust the crossover..

1)  Turn OFF the subsonic filter

The idea is to match the crossover points - like the graph in my previous post.

Let me know if that helps at all. 

And like I said - recheck your wiring.  If one subwoofer moves the wrong direction it could cause cancellation problems.

Ok.... a crossover cuts frequencies so the speaker doesn't play them.  It just doesn't stop playing them ---- it reduces at a slope. 

1 Octave is a doubling in frequency....

A decibel is the unit used to describe SPL. 

So, for 6db / octave slope the sound is 6db quieter from say 40-80hz. 

Does this work for you?

I agree with yall solutions but i got one thought. from my previous experiences with multi driver/single chamber boxes that are sealed is that , well its just not good,.Speakers come with a certain size enclosure needed to give the correct air pressure internally in which the speaker can compress. when you got four subs pressing against each other it causes it to not preform up to par. if you feel the box is still big though , or in the future , then try using polyfill ( like for pillows) it causes the resistance inside to increase making to act like a smaller enclosure.

If im just blowing smoke someone tell me please..