I have been staying out as much as possible the last year as when I chime in it tends to end the chat!!!
KLM = Kapton Low Mass - a "Rolls Royce" grade of the original Kapton specs as used by Apogee. When used without a number this denotes "0" type adhesive on the kapton, coated here in house, an expensive premium chemical grade. I have found this adhesive to be excellent for the bass ribbons, superior to the original construction used by Spiegel/Bloom/Walker/Schuman for their ribbon construction.
KLM5 = Kapton Low Mass, but with the 5th type of adhesive I developed for use primarily with MRTW constructions, again coated in house here. This is a very expensive adhesive, chemically similar but even better. Of course has many of the "0" properties, taken to new levels of tolerance.
KLM2 - worth a mention as it is still the current grade of tweeter-only ribbons offered. This is a good adhesive "2", better than the original 1980's chemistry but completely different. A nice MRTW solution.
Crossovers. The crossovers do not need modification with any of these ribbons as the foil work is absolutely blueprint accurate to the original construction, grade, metal composition/construction of the original foils.
XLM - this is a lighter mass version of the KLM kapton.
Advice. This will read like an advert but xover mods and "extras" will take a back seat to a ribbon upgrade vs a perfect original speaker, by design. This is of course my opinion, some have shared this here. None of this is based on myth - as all ribbon work I have done here for the classic or new Apogee's has been based on sound science and engineering. Cost was never a factor during prototype work - the emphasis was always on getting things right! In order of effect, all imho;-
1) Bass and MRTW ribbons
2) Magnet alignment. More of a joint first place really - tolerances here are equally important to ribbon topology tolerances. If they are not right, then the result will be compromised.
3) Frame bracing. Keep the frames quieter than when made and the sound will be more faithful from the ribbons
4) Stands. Brace work should be complimentary to the bracing of the cases.
5) Settle on a configuration and remove the switch, and solder the entire circuit, at the same time replacing the brass terminals with copper ones - or hard-wire to set leads from the speaker.
6) Inductors. Pot in conductive resin, or replace with potted or foil equivalents, measured from the Inductor - NOT whet is written on it!
7) Capacitors. Upgrades to be heard here - no advice offered, everybody has their favourite cap!!
This should draw some comment
Take care - Graz