Hi,
I know the midi doc is not very up to date.
Don't hesitate to ask any questions if you need more details.
Is there any new development in the MIDI list?
I think it would be very handy if there where more deep MIDI control over the FM.
So you could just use it like the OP6 with its sliders. Just add a LaunchControlXL to it and here you go.

Of course it would be the best, if the Preen had a MIDI learn feature, so there would not be a hardcoded list and you could just do it learn what is needed.