You have a mess on your hands.
First of all ribbons are not high spl speakers and are permanently damaged by over driving. These speakers are for Mozart and small Jazz groups and not rock.
The major problem with ribbons is that they destroy amps due to very low impedance. The wags say they convert good amps to "smoker amps."
The passive crossover is at 150 Hz. The crossover is inefficient as it uses resistors to increase the resistance to the ribbon to prevent blowing amps.
Hers is the crossover circuit.
First note that the woofer and ribbon are in reverse polarity.
The low pass crossover is third order 18db per octave. There is an L-pad in the woofer circuit which is a big no no. That is probably why the bass response of these speakers is so wooly and muddy. Bi-amping would help this issue, although enclosure volume could change as eliminating it will change T/S parameters.
The high pass is complex. It is basically also third order but with a lot of equalization. There are also resistors raising impedance and wasting a lot of power.
There is HF equalization and a tuned rejector circuit whose output is controlled by a couple of L-pads.
There is a tuned resonant acceptor circuit across the ribbon, presumably to remove a peak in the response.
Now you will never come close to duplicating this circuit with an off the shelf electronic crossover, no matter what you do.
You will need to duplicate the response of this high pass exactly with a unique high pass crossover.
Unless the amp driving the ribbon is stable below 1 ohm, I suspect you will have to add a hefty power rated resistor in series with the ribbon, to stop the amp going into protection and or blowing up.
My basic opinion is that these types of ribbon speakers are not practical and not worth the trouble. I know these speakers well and frankly, I don't think they are good enough to spend time effort and money to work though the boat loads of problems you have already encountered and many others have before you.