haha, no what helotaxi is talking about is is having the space built for 2 subs necessary volume.
having cutouts for 4 subs made.
mounting them im pairs face to face. and wiring the out of phase of one another so that as one pushes the other pulls.
it effectively reduces the vas by one half. (reducing size necesarry by 1/2 also)
so you have 4 pairs acting as 4 single units in what is now an adequate space for them.
so as he stated 8 subs in the space for 2 with the output of 4.
hope that makes sense?