I was the sound librarian at Sounddogs.com when they first acquired the Soundstorm library.
I was in charge of cleaning up the metadata. I can confirm that the old naming structure ("S_123456.wav") is indeed the former naming scheme before I applied the English names used in the library.
There was actually an Excel database that related the old names to new ones. I used it rename the entire library with an app (Soundminer, at the time, wasn't a good option for renaming filenames).
Rob Nokes (owner of Sounddogs.com) may still have it kicking around. I'd suggest contacting him directly. Tell him you're looking for an "Excel database relating the legacy Soundstorm numbered filenames to the current English names," and that may help you. Contact Rob Nokes
I believe I also embedded the original filenames in the Soundminer "notes" field for safekeeping, so that's another route you can take as well.
PS - Email me via jetstreaming.org I can answer any other questions - I check back here only occasionally.