The .stx file has indeed been created by the Roland Dr. Stika program that ships with the Roland Stika. If you have Roland CutStudio you can import the file into that program, but you can't save it from there with any other file extension except a .cst file (the default Roland CutStudio file type).
If you don't have that program either, send me the file. I just successfully opened a .stx file in Roland CutStudio and was able to copy and paste into CorelDraw, at which point I can save it as any type of file you need.
Gene