I have had cabs with both the Eminence 3015 and Faital 15PR400 and likewise prefer the way the Faital sounds. I built this 15/5 Faital cab with mid driver and have been very pleased with it.
Faital 15/5 Build
I built in a -2dB L-pad with switch for the mid driver and another switch to bypass the crossover and run the 15 full range. This allows three different modes to run the cab. Even though the 15PR400 has good high end extension for a 15 (noticeably more than the 3015) it still sounds too dark for me so I never use it. You can definitely use a tweeter like the Greenboy Dually T does. I won't speculate on the details of that crossover/filter. What I found was that crossing over just under 1500 Hz to that Faital M5N8-80 allows the 15" to provide the meat of the mids and lets the 5" provide what is missing. That 5" tops out between 6-8 kHz which pretty well covers what a bass puts out. -2dB attenuation provides the right mid balance since your ear is pretty sensitive to that frequency range. That mid makes a difference in a good way. It's smooth, present, voiced well, sounds good with overdrive, and really improves dispersion.
The 15PR400 also sounds more musical than the 3015 to me when driven hard. It compresses a bit but keeps the bottom solid.