I placed my AN15s back in my system and paired them with the Faital driver. The 18s DEFINITELY can't handle above 100hz. They're awesome subs for certain, but midbass is not their forte. The AN15s totally trounce them in terms of naturalness and speed of the midbass. Much less edgy and far more effortless and uncompressed. I'll potentially build a set of amps for the subs and use them for below 100hZ. Or maybe I'll just sell them because I'm fairly happy with the AN15s until the Alnico version comes out. The 18s are monsters though, really great subs, just don't know if I need them at the moment.
The FP driver is stellar though. I ran some tests on fuzzmeasure and it's EXTREMELY low distortion across its frequency band down to about 400hz. It's about -70dB compared to the last compression driver (a B&C driver) I tested, which was up at -50dB harmonic distortion. The neat thing is the FP driver's 2nd and third harmonic distortion graphs are identically low. Proof is in the listening -- sounds fantastic.