Honestly, if this gear landed in my lap, I would not bother using a passive crossover.

I would set the F12s up on my main amplifier as a full range set and get a small plate amp from Parts Express so the Kappa drivers will serve more of a subwoofer function.
The plate amp will have an electronic crossover built in along with some adjustability to help in "tuning" things.

What ever you are using for a main amplifier, you would hook the speaker output to the Lii Audio F12s just like normal and add an additional cable from that same output to the plate amp High level input (speaker level input) which will then drive the plate amp with the same signal entering your F12 main speakers.


However if you really want to create a passive crossover network between the two, you can use an online calculator to get you close. Well not really close unless you get lucky, but within 40% to 50% accurate and it would be a safe option.
Here's one I have used to get started in the past. There are dozens of others out there:

https://www.omnicalculator.com/physics/crossover


Thing is, once you buy a pair of high quality coils large enough to passively cross over the Kappa drivers down low enough to not interfere with your full range drivers and a nice pair of capacitors for the F12s, you've already spent a good bit of money.

If you go with a 12dB/octave crossover it becomes even more complicated and the parts count doubles or more since we have not talked about resistors to balance the two together yet.

But this is why I recommend a simple plate amp for the Kappas and be done.

This is one of the most popular plate amps from Parts Express and I have used this same one in several installs over the recent years.

https://www.parts-express.com/Dayton-Audio-SA100-100W-Subwoofer-Amplifier-300-80...

Here is what I got just plugging in some perfunctory figures into the calculator.
This is simplest possible 12dB/octave crossover design.

I would run the Lii F12 wide open and use a simple 10mh or 12mh air core inductor with the Kappa 12a.

The real challenge here seems to be the Kappa 12a.  Eminence shows that it goes down to only 65hz, and with a Qts of 0.27 on an open baffle, it’s not going to produce any real bass.  An Eminence Alpha 15a would be the ideal open baffle woofer.

Best wishes and good luck with your project.