Yes, It will work on the original Specy rx's. I tried it back then to verify it did for a few buddy that had specy issues.
If I had access to a few old specy rx's I could bind the Reacts I still have to it I'm sure. But I don't have any, nor do any of my rc buddies anymore that I am aware of.

And yes, the DSSS mode is a different way to communicate, which is why they bind with the original Spectrum rx's.
Nomadio's transmission rate was too fast, even for the Futaba rx's at the time. Which is why Nomadio called the DSS (Da Slow Mode). lol
The Transmission rate had to be limited so it would communicate with them.