Ummmmmmmmm, where do you start? You want to get a baseline for the passive tuning. You must talk to Brian about the original PR mass, but honestly, I don't think he keeps written records of the mass preloading on the prs. then there is the problem of comparing the current pr appearances vs. whatevr mass brian says they should have. you might want to consider just buying new pr's if b offers them. This subject of the pr mass is probably the single most important item because if you don't have a baseline you will be shoooting in the dark literally forever. I'd would say if you don't get an accurate pr mass baseline, each & every other parameter will have no baseline & hence no foundation. in other words: do not waste time listening to them or tuning them till you have the pr mass totally sorted, at least for a baseline. Then, as I used to offer in my personal instructions, label each speaker A & B, or blue/red, (don't use L/R because, though your speakers are normally dedicated L/R, they could theoretically be reversed if placed very close together). Get 2 envelopes & label them to match each speaker. As you remove mass, place it in the matching envelope. That way you can easily return to the baseline by replacing the mass on the pr from whence it was removed.
Also, make sure you ask b about how tightly the fiberglass was loaded at the plant, & compare to your speakers. It is possible some might have been removed at some time & you may need to restuf or redistribute.
My personal opinion is that the RM40, with the neo ribbons, is better (above the bass range) than the FF3 SRE active w/the single B-G ribbon mid (I owned both spkrs for over a year). Don't take that the wrong way, but rather as a recommendation to consider upgrading your old B-G single ribbon to the 6x neo ribbons. The difference is simply earth shaking. I've heard that speaker, & it is simply an entirely different beast from the single B-G ribbon model.
One last thing: if you upgrade the mids, & somehow replaced the 3x spirals with the HET, you would have a midrange/treble ribbon array with a sensitivity of about 94 dB, with very high output levels from as little as 25W (think tubes). Just be careful: all tube amps, according to a source who builds some of the best tube transformers for a living, must be fed a load for all signals at the input. Meaning don't feed a fullrange signal to a tube amp at the input, then omit presenting it a bass range load, relying on the midrange's passive high pass filter. That is a no-no.
