Turns out there is a Castlevania SOTN Decompiliation project out there. The project aims to Decompile the PS1 version of the game.
Quote from the Developer Xeeynamo's Github page..
A work-in-progress decompilation of Castlevania Symphony of the Night for PlayStation 1. It aims to recreate the source code from the existing binaries using static and/or dynamic analysis. The code compiles byte-for-byte to the same binaries of the game, effectively being a matching decompilation. Currently it only supports the US version of the game SLUS-00067.
How cool is that! SOTN is my favorite Castlevania game, hopefully once the project is complete they'll add the Saturn only levels in, though that's probably only the tip of what they could add
Github