DS-Xtreme save file compatibility
DS-X Save Files
The DS-Xtreme uses custom compressed save files. However these can be converted into RAW .sav files (compatible with the Supercard series and importable into pretty much any Game manager software) by stripping off the first 24 bytes in a HEX editor and renaming the resulting file to .gz. You should then be able to decompress the save file with your normal archive software.
Eventually you could use this tool to convert the DS-Xtreme save to an "R4", "M3" or equivalent "pure" save format.