Did somebody know (or have an idea) of what kind of piezo installation are in the Hobo king standard CBG played by Pinecone Fletcher (http://www.hoboking.com/)

In the interview (see video 1) is talking about a double piezo transducer enhanced just made for his guitars. The sound is incredibly warm.

The details given are "Hobo King MK II pickup system. Frequency optimized for Hobo King cigar box guitars."

What is the secret? (ok if we know it it's no more a secret! ;0) An internal pre-amp? (as there are no other controls of the sound on the guitar itself)