I'm guessing placement and loudness.
That would certainly be two obvious places to start guessing as to a difference.
Is he running the sub gain at a setting greater than yours?
Is his receiver bumping up the sub signal gain?
Does he have the sub closer to walls?
Three 8" drivers does provide more surface area for air movement vs a single 12" (RMS is not a useful spec).
A few years back i had a friend who was keen on getting the most bass as cheaply as he could. I steered him towards the SVS line and he hasn't fathomed looking anywhere else since, although he has contemplated swapping out his speakers for some others. We settled on a SVS PCi 16-40 and did a comparison some time back with the Axiom EP350.
My thoughts were
posted wayyy back here. 
