Maybe difficult to change a bad design (and saving the woofers). I don't know if this is the case. My point is, you only need to know the inside enclosure volume to work with/for (new drivers, woofers) in a new designed working kit for specified volume. What means totally new loudspeakers or saving the enclosures. Can you elaborate?! It's my understanding you have to measure for output, phase and impedance for drivers (frd/zma's) if you plan in using them and make a new crossover.
The best advice is before to change anything, is to tweak the crossover.
Can take the schematic, two photos of the board, on the components and the other face ? It should be very simple.
The tweeter can be good but the mariage of the transducters, not
Honnestly, it's better to make an better design with better drivers.
There are a pair of good Gradient tweeters in Jamo Classic 6, no need to replace IMHO. The woofers are nice too. Vifa XT25 is no any better, it's only different and maybe even worse (personally I dislike XT25. ). The worst part of these speakers are crossovers, and used parts are very low quality. My advice is: leave the speakers alone and tweak crossovers. Or better get rid of the crossovers at all and build new from scratch using good quality parts.
The treble of the woofers is not enough well filtered. Too much bad treble from them, sure you want to change the tweeter, but it is not the problem. You can try this crossover on the woofers. You will have a better treble.