Actually @jackd, you have it backwards. Brian Ding of Rythmik Audio designed the patented Direct Servo-Feedback circuit and amplifier found in the Rythmik plate amps, and has those plate amps manufactured in China. They all come into the U.S. through Rythmik, Brian then sending Danny Richie of GR Research some to sell with his sub kits.
Danny was already offering a sub kit when he learned of Brian and his new Servo-Feedback design. It occurred to Danny that Brian’s S-F circuit combined with Danny’s idea for an OB/Dipole sub would produce a new state-of-the-art sub. They got together (both are located in Texas) and came up with the finished design of an OB/Dipole sub, as well as some sub drivers. Brian offers complete subs (sealed and ported) and the OB/Dipole Sub kit, Danny DIY sub (sealed and the OB/Dipole) kits only, as well as many loudspeaker kits.