DANCE2000 extra registers

I noticed that the NintendulatorNRS implementation of mapper 518 (UNL-DANCE2000) uses a few registers not mentioned in the wiki. Register $5300 is DAC sound samples related. And registers $5500 and $5600 is for some sort of data persistence. I am particularly interested in the data persistence mechanism. What Subor hardware is this emulating?

Yikes! Does that mean there is software available on floppies for that Subor PC? Or, are the floppies just for saving?

There is floppy-based software for the SB97, but no disk has been found in working condition so far.

And as this video, originally linked to in the thread I mentioned, shows, there seem to have been specialized cartridges for this computer that make use of its speech chip, and possibly other resources. The cartridge shown in that video at 8:20 seems to be undumped.