Eek, thanks for trying! Sorry it didn't work out. I'm not sure what to try next at this point. We're starting to reach the limit of what I know how to do

If anyone else is interested in figuring out what the heck needs to be done, the file I linked contains extensions with the DRVR resources I extracted from the Mac OS ROM file.

It's very interesting that the normal .Sony driver doesn't appear in the driver list if you use the Sony extension. I wonder if that's a clue. Maybe that one is indeed the correct one and it's having trouble loading for whatever reason.