Hmmmmm....wonder if maybe the JBL was producing more of a boomy bass which only "sounded" like "more" bass than the cleaner sound of the 350??

Also wonder if the noise(bang, bang, bang)you are hearing is the driver bottoming out?(my old 10" Peerless driver powered by a 150W amp, although rated at 200W, would, when plotted, indicate running out of travel at about 85W, albeit in a sealed cabinet)!!

I haven't the foggiest though, cause I've never had a "Killer Sub"(with a port,even)to be able to add much relavent input