i believe the 52" ribbons are sourced from bohlendeer-graebener, but i'm not sure - ask brian, he'll give ya the straight poop. i *do* know that there were relatively recent changes to the magnets for the ribbons on ff1 & ff3 (the sre-version is what you're considering.) also, i tink the *mega-woofer* option, that you're talking about, has been in use for some time now - again, brian will help w/info here.
i've always thought the ff3 would mate well w/my pair of larger vmps subs (older upright style, which i upgraded w/the megawoofers) - i obviously don't need the better bass response of the ff1's! :>) but, brian has recently released a new model, the rm40 - ~5'6" tall, 12" wide, ~250 lbs, that's much less a visual distraction, due to its not having the *sre* ribbon panel affixed to the side. and, according to one of the vmps dealers that has posted to harmonic discord, its sound is better than the 1st version of the ff3-sre, at ~half the retail price. and, dealers *will* haggle on price... :>) there's a dealer local to me that carries vmps & has the rm40's (where i got my subs), & even the wife is buggin' me to hear them! i'm afraid to go until i know i can cover the costs... ;~) but they offer it in a kit version for a bit less, so w/a decent dealer price, i just may be able to swing it! :>)
doug s.