Rat....With the SVS cylinders it's about extension vs. SPLs. With the 25-31 you get max SPL but only down to 25Hz (typically a little more in room response). With the 20-39 you get 20Hz extension but a few less dBs. With the 16-46 you get the deepest bass but again a few less dBs than the 20-39. Most people find the 20-39 a good compromise because you get close to the level of SPLs of the 25-31 but you get the extension to 20Hz or more for movies. As far as the PCi vs. plus it's 525 watt amp vs. the 320 watt amp. I have the PB12-ISD (320 watt amp) in my 15'x15'x15' at 35% gain and I love it. It all depends on how big your room is (and you have a big room) and how much you really want to feel it vs, hear it. I would email SVS/HSU/Axiom with your expectations and room dimensions. All will be more than happy to assist you in getting the best sub for your needs.
I initially ordered a PCi but decided I wanted the box sub for *cough* decor reasons.
Typical guy response to tall cylinder sub: "That is WAY cool!"
Typical gal response to tall cylinder sub: "Get that water heater out of the living room!"
