I guess I should be a bit more clear on what I am looking for.
I am familiar with isobaric subs, and the technical reasons behind them. I understand why ACI designed the Saturns - drivers of that vintage required a huge volume to work properly. Modern drivers, not so much. Drivers have come a very long ways from the late 1980's. What I am really trying to figure out is should I try to get 4 "new" drivers that will be compatible in my current enclosure, or should I find 2 drivers that will be equally as good? I have not looked into components for ages, and am totally out of the loop on what would be good today. I also understand that 4 drivers will require a lot more power than just 2, which is why I am running 3 Adcom amps currently, 2x GFA555 for the Saturns, and a GFS545 for the Sapphires. Plenty of power there. Plus, if I "have" to, I can go buy another Adcom quite easily - always many listed for sale.
So opinions?