Thanks guys... the room is relatively large and is a dedicated home theater. I should post some pics. It may well be that I'm just experiencing some upgrade-itis.
I figured it would be pretty impractical to do the upgrade, although I will contact DefTech directly next week just to anno...ask them if there's anything to do. Maybe it's just that the sub amps need a recap after 20 years and hundreds and hundreds of hours of use.
I did drop $2000 1995? 97? dollars on them plus another 2 grand for the CLR 2000 and BPX surrounds. That was painful for 30 year old me back then. I think I've gotten my money's worth. I spent hours with test discs and SPL meters and countless beers given to audio engineers to get the room just right. It helped I worked with a bunch of enthusiastic audio engineers at the time.
Bottom line... you guys are right. I have a false wall in the front of the room so a free-air sub or subs could possibly be built into it. I would have to do the numbers to get the volume of the enclosure....but it would be large considering 12 foot ceilings and 25 foot width plus about 10 inches from the actual wall to the false wall.... but that's another thread.