It uses an FPGA chip whose logic is determined by software. I understand it to be like a blank slate. Ted Smith writes the code. And there are periodic upgrades. It just keeps getting better and better. It sounds as good as the most expensive R2R ladder DACs that cost 10-20 times more, or so it has been stated by those who own both kinds.
AFAIK, Chord is the only other company using an FPGA approach. But Chord doesn't have Ted Smith. And PS Audio provides exemplary customer support; maybe Chord does, as well, but I don't know much about that company.