I've been using my PreenFM2 since a few years now, and honestly i never became an FM specialist
But when i started, i didn't knew anything about it and now it's obviously a bit more clear. But I will never be able to know what kind of operator algorythm i should use or what setting i should do on the modulation matrix to achieve a particular type of sound.
But what i still was able to use it since the beginning.
I started byt downloading lots of DX7 banks that are lying around in the net, browsing them and selecting my favourite presets.
In a second time I started tweaking them to get them closer to my sound tastes.
And now I can start a sound from scratch, but only by accepting that I'm not trying to reach something in particular. Just experimenting until something l like happen.
And somethimes it can be enough to make music.