I'm probably too late to be useful, but it might be worth it in the future. I used inexpensive drivers in waveguides/horms for the tweeter and the mid. I used Daytom AMT Pro and the above-mentioned SB acoustics 6in ceramic driver, and 15in FaitalPro I got used. Total driver cost/speaker is about $600. Extremely low distortion, which I measured, per driver (using Hypex 3-way plate amp, with DSP - note a notch at 40Hz to tame the dominant room resonance). I first set the output to be about 100 dB at 2 meters in midrange (simulating 106dB/1m), showing distortion at that location, then I moved the microphone to 4in from the bass driver cap, or 4in from the mouth of mid and tweeter horns. Distortion drops when measuring at 4in, removing many of the room effects, while also smoothing frequency response. It is informative to notice how the frequency response gets progressively smoother going from low to high frequencies (when compared to the 4in measurements). Waterfalls show absence of resonances, except at lowest frequencies when even at 4in you get room modes.
This is intended to be a center channel speaker in a dedicated media room, so deep bass was not a concern, but high output at low distortion, and good directionality down to low-ish frequencies was, thus the waveguides. The main speakers have much larger waveguides, going down to about 160Hz.
Final photos are of the speaker during buiding, and with the tweeter and the bass sections completed.