Why all this just for stereo FM?
It's phase modulation, not frequency modulation, but never mind... It's definitely not radio. So what is it? Why use some old synthesiser format that many people might argue is obsolete? First, is the MiniMoog obsolete? Good instruments are never obsolete. Second, do you need compatibility? The DX7 set an exact standard, one so well regarded that it's been preserved by many other instruments built decades later, even if they add, interpret or change things that prevent them saving data in the original format.
If you want to make sounds that are compatible with all of those instruments, you need to work within that format, then let owners of those instruments do what they want with the result. You might search long and hard to find a tool that will create and edit the original format as quickly and accurately as this one will do it, and most of those won't be free, or may not run on as many systems as this one will, and few if any were ever optimised for making stereo sounds. The power of Yamaha's DX synthesis is legendary, but in stereo forms it has a realism that few synthesis methods can beat.