We can invent any set of creators for the technology, as long as we have them complete their research by the late 1980s at the very least and put it in practical and public use aboard DY-100 spacecraft. I'd just enjoy having the wild speculation be anchored and even limited by onscreen facts.
Since those aren't many, and (as seen) can be endlessly debated, I might throw in some classic noncanon material. The old Goldstein/Sternbach Spaceflight Chronology
is silent on the actual issue, but mentions the Earth-Saturn probe of "Tomorrow is Yesterday" fame discovering signs of alien presence on several of the small moons (ring fragments) of the planet. The book only speaks of "signs of mining", but perhaps there was a Stasis Box there that the aliens had searched for and failed to find? Or had finally uncovered, opened, and then abandoned, perhaps because what was inside had killed them? The box and the rest of the contents would now be open for humans to stumble on (and secretly deliver to their government while the internationally published mission report would only mention the alien mining).
This is the very first proof of alien life in the book (there's a SETI breakthrough a decade later, and a meeting with aliens after a sublight interstellar flight to Alpha Centauri in 2048), and obviously doesn't explain DY-100, but could serve as the "key" that unlocks the mystery of how those long-dead Augment scientists originally developed the DY-100 AG system.
Personally, I still prefer the idea that the flying belt from the Stasis Box was some ancient discovery that played no role in the local development of AG systems on various planets, but could be established as the earliest application of AG and thus the "spiritual forefather" - much like the Pyramids, the Stonehenge or Göpekli Tepe could be considered the basis of later construction including works whose makers had never heard of those early achievements