I know there hasn't been much activity on this thread recently, although there have been a few references to it in other threads. As previously explained, the next stage here is a lightweight design using neo drivers. As an interim step, I've just revised Chienmort's Beyma system by swapping out his Celestion ceramic compression driver for a neo one. The sound hasn't really changed, but we've saved about 1.5kg thanks to the new compression driver and simplified crossover.
Phil asked me how it measures, and the easiest way of showing him is to post the measurement here. So.....
I've been able to compare this cab with my own version fitted with the Faital Pro 12PR320 (and the same compression driver) and the Faital Pro cab is noticeably better in a number of areas. I'm therefore not going to publish any details of this interim system, but will go straight to the Faital Pro system once I have revisited the crossover to see if I can't make it a bit simpler.
As you can see from the frequency response curve, this design is as FRFR as you like.