Hi Mike, Yes, I used a respirator for the second speaker, didn't smell a thing, and didn't get stoned. MEK is not good for you. Thankfully, the damn roofing membrane is all used up and may never return. Such a pain to work with, but it does take down the wood ring a lot though... They make a self-adhesive version, but I bet it doesn't stick good enough for vertical applications of small pieces.
In the Tech Talk discussion that created this crossover, there was talk of notches and impedance correction, but Zilch didn't choose those for the final XO. The rising CD impedance's effect will vary with the damping ability of the amps, so it might benefit the HF to leave it untamed for the SS amp, and add it for the tube amps. Flattening woofer impedance will change the crossover parts values, but might sound better by making less woofer in the upper mids. It's all out there to try.
Are you still planning to build 4pi Mike?