It is my understanding that piezos are self limiting with regard to low frequency, that is, the impedance of the driver makes it act as its own high pass filter. This would make the crossover very simple. I think that you could get away with 1 inductor on the woofer and a resistor across the terminals of the piezo.

It's too bad that the spec sheets are not available. I'd like to see what rate the 800Hz piezo rolls off at. I'd also like to see how flat the response is. Of course, at the price its reasonable to just give it a try.

I’m not familiar with the Pyle Drivers but in looking them over, the PYM1555 (292-236), PYM15128 (292-240, a little pricey), and PYM1578 (292-238) all look like they might be a good match. Also, the Dayton "Cast Frame Driver w/ 4" Voice Coil" (295-080) looks like it would work well in this application. It's a little pricey but still in range.

Good info on the horn. My guess is that you would get the best performance with the 270-099 would sound best because it appears to have a much smoother transition in the horn.

I also like the KISS aroach.

Dave