Wow, this has come back from the dead!
It's a crying shame that Audax have dropped out of the diy market. Aerogel was great to start with, and I suspect, had R&D carried on, now be the best cone material available.
I'm suprised you liked crossing over the Z0s so low. In my experience, they started to sound a little strained below about 200Hz. With the aerogel PR240s being quite happy up to about 1.5K, I ended up using a second order crossover at about 300Hz, much the same as you!
What is the reference of this so rare Audax tweeter?