To the original poster, I concur with about everything everyone else has said, and feel it's all-the-above. The build quality is top tier, the basic acoustic instrument itself has "that sound," and the Bartolinis put the tone in a particular place.
The coating is definitely a factor. But the neck's dynamics are as much a factor, probably the most. In comparison, my (dearly departed stolen) Rapture J2-5 felt almost like a Fender neck compared to the Pentabuzz, and the Rapture has an extremely thin neck!!
The Pentabuzz neck definitely flexes more than the Rapture did, too. Not to say in a bad way--at all--but that's part of the sound. You can move it around, it's thin thin. I think if you have one, you will identify with that sweet spot where you are really feeling the instrument acoustically, and you are definitely feeling attacks resonate through that neck.
You understand why it's called a Buzz when you start becoming accustomed to the coating. You can open up finger pressure slightly and get a lot of resonance. You can burn off some sustain by letting it "buzz" a bit, and open up the "mwahh" sound in a controlled way. The Barts smooth it over, and I understand completely why they're a component of the overall design.
Also, if you take MP at his word, and set it up as close as they suggest, it's extremely buzzy low on the neck. In that context, the Pentabuzz is actually very nice for the E-A range on the B string. You can use the very buzzy range on the E string to great effect if you dig in hard, and if you need a more pure tone, just pick it up on the B. Great string to string balance!
It took me a while to trust the bass, actually. What I eventually realized is that I wanted stainless strings, but didn't want to tear up the fretboard. I put Black Beauties on it, and for a couple of days I wondered if they were overkill, but then they settled in and I am very happy with the sound. They are perfect on the fingerboard, actually far less friction against it than nickels...noticeably less. So, that was a real win-win for me. With nickel rounds, I felt the Pentabuzz was very refined and bloomy and warm. With the Black Beauties, there is a wider tonal range of attack, and just a bit more tension. I am going to stick through a few sets and see if I continue liking them this much. But if anyone has wanted to try them, I can report so far so good...
I have to confess, I've never tried Pedulla's strings. Maybe I'm totally missing the boat...ha!
Bruce Richardson, Dallas TX...Pedulla Pentabuzz, Rapture PJ-5, & Rapture J2-5, TC RH450 w/Bag End & Bergantino cabs.