The FPGA based DAC was first created by Andreas Koch at Playback Designs. Everyone else is following his coattails. Nagra decided to just buy the boards from PBD instead of creating their own, such as PS Audio (Ted Smith). I read somewhere that Ted spent time with Andreas to learn how to do FPGA.
These 2 videos are informative on the history of digital.
E89: Andreas Koch and Digital Recording (youtube.com)
E93: More with Andreas Koch! (youtube.com)
I think doing digital correctly is complicated and I question the credentials of almost every company charging an arm and a leg for their DACs. At least with Andreas I can justify paying for his knowledge.
One reason I bought the Schitt Yggi+ LIM and the OG was because of the long digital history of the designer, Mike Moffat.
I will get one more DAC in the future and that will be either a PBD or Rockna, because of the designers.
BTW - the implementation of the Tambaqui was first done around 2006 by Bruno P. This was for the Makua preamp’s optional DAC module. The Tambaqui was the result of customers asking for an external DAC.
There was in interview on ASR web site were Bruno said this