If you have all the answers why did you start this thread at all? Just because my (and others) comments don't jive with what you wanted to hear doesn't make them invalid.
What is your best SPL score to date? What org? Where is the mic? Doors/windows sealed or open?
Sub with super stiff suspension is not musical period. Tuning @ 40hz with that sub is not musical. I've actually built subs that'll play that far below tuning without bottoming out and let me tell you they're not musical and they're not efficient, at least not efficient over anything other than a very very narrow bandwidth.
If you want to play low, tune box low, if you want to play fartbox tune high and don't pretend it's musical. Pick one and run with it, or try to be somewhere in between and be happy with it, but don't try to be in between and pretend it'll do either particularly well.
Get rid of the Soundstream amps if you want to get loud or sound good, they will do neither well. Most of the guys up my way gained big when they got rid of soundstream amps and got into something better.