I too am asking myself the sub replacement question. I have an older 10" klipsch sub with a passive radiator. My problem is a firecracker loud pop during explosions on recent high energy dvds. After removing the y-splitter which is part of monster's dedicated sub cable the problem diminished. Klipsch tech support suggested looking for physical damage to the active and passive cones. They also stated that subs built during the dolby pro-logic era may not be capable of handling the excursion of modern DD and DTS sound tracks. I am now trying their suggestion of reducing the 955's channel trim on the sub to -15db maximum and using the sub's own power level controls for adjustment. They mentioned the R.S. db meter as being unsatisfactory for sub level adjustment, that I should calibrate "by ear" for the most pleasing level.
My system includes the 950,755, and B&W CDM-NT's all around. Their dedicated center channel (a large and heavyweight monster) and the wall hanging surrounds are awesome!
Any comments or suggestions?