Hey, so I looked at the review and the close-mic measurements. I have further thoughts. About the best you could do is clean up the tweeter caps OR ...
a fully active conversion. Get a 2-channel plate amp with DSP crossover. I _think_ you could push the woofers up a little higher, to say 3 kHz, and clean up the tweeter response by a lot. You need to measure and experiment. Measure the output of the woofers in front of the tweeter angle to see how the arrays work off axis.