Chose 12db/oct and around 1000Hz for the 2121H to TD-4002, and was stuck with 24db/Oct (because of crossover) and chose around 200Hz for the 2231H to 2121H. This got me the flattest response I could get, haven't played around with phase that much.
So it's sounding fairly well integrated at the moment with regards to freq and SPL, but still not quite sure I prefer it. I'll need to listen a bit more to understand.
While it does have that nice clarity from the TAD, the whole experience is "Different". It kind of isn't JBL I guess, as discussed before. Perhaps it's lacking some presence and punch. It seems the TAD just has a different sonic character and this perhaps doesn't match the other drivers as well as when using the 2420 etc. And/or when Tri-amping the differences in amps, makes it hard to get the whole thing to come together.
My gut feel is that in the stock 4343 the "whole is greater than the sum of the parts" and this is due to the genius of those that designed it. Adding a "Better" driver into the mix may not result in a better overall result, because it's not as well matched in character and the compromises in tri-amping may outweigh the benefits. I'm not even sure that a passive network could be designed for this driver combination to make the whole greater than the sum of the parts, becuase the TADs character just doesnt match, it's too delicate and sweet. The TAD is lovely, I do love when you're picking up so much detail you kind of hear the echo of studio at certain parts in songs that you never heard before.
If I could get just a little more of that berylium detail in the 2420 but still maintain the punch etc I think this would be the best overall solution. Will keep playing.