Load the pre assigned CC# patch for FMDrive 1.25 in place of the init program preset (preset 1)
named : F-MDRIVE YM2612 - Init GenMDM 102.fxp
right click "load instrument" on PROGRAM (bottom right)
The CC# will remain attached for this instance even if you change the program.
All the CC# are sent also sent on program change.

example for control over YM2612 Channel 1

1 MIDI TRACK  >> (NOTES DATA) SEND to CH1 >> GENMDM
1 VST TRACK (With FMDrive) CC AUTOMATION SEND to ch1 >> GENMDM
and so on... 

Use the +1 or -1 octave MIDI transpose in your DAW / Host on the MIDI channel used for the note (if you want the same octave on both FMDrive and GenMDM, there is a -1 or +1 octave difference in the implementation)

There is one thing in GENMDM, the velocity data is send to the TL volume, but all of them not only the carrier operators as it should be.
So first thing you should do is make sure all notes velocity is maxed out, if you use a keyboard to record the notes, be sure that your keyboard is set to always max velocity.