We doubt only one thing in your post... that you will lose interest!

The Reference Manual will be posted (sorry if this sounds trite and/or flippant, but it is not) as soon as it is finished. Truly.
In the meantime, we have this forum where you can ask questions and hopefully, receive informative answers. On the FM scale from simple to complex, the FM-X engine in the Montage very much resembles the 8 Voiced Operators in the FS1R engine. For those not familiar with this late 1990s rack module, it featured 8 Voiced (musical) and 8 Unvoiced (noise) Operators that combined to make a formant engine... which was close to being able to "speak", as in create understandable words... A combination of fixed frequency sounds (noise components) for consonants, and musical tones for the vowel sounds. Well, take the musical side of the FS1R (sorry no formant synthesis here), with the 8 Voiced Operators, and the 88 Algorithms and combine that with the Motion Control engine and you have what's new about FM-X.That and the increased speed of envelopes, filters, effects, etc., etc.
The combination of FM + Motion Control = FM-X
And for those that enjoy and understand FM, this the exciting thing... Imagine modifying a Modulator ... In FM you know the Modulator's influence on the Carrier causes the resulting tone to change. You can use virtually anything to modify an Operator... Both internal and external sources are available. It could be the amplitude of another Part, an arpeggio, your drummer's kick drum, your guitarist's rhythm, any microphone input... Almost anything you try creates something interesting, and opens another doorway of endless possibilities!
First thing I tried (cause I wanted to see what would happen) was using an arpeggio's rhythmic pattern to influence the output of Operators 5 and 7 (which were Modulators) and the results were amazing... almost anything creates a dynamic, useable and interesting result. Unlike RCM which, frankly, had a small window of functionality (using audio as an input to the Operator - which as you probably know went straight to noise. The more complex the modulator the quicker its influence on a Carrier turns to chaos, noise).
The
Super Knob is the gateway into
Motion Control (assigning the influence to a physical controller), then you can even build your own
Motion Control Sequences and use those to modify the results, and the
Envelope Follower which allows you to use the "attack-decay-sustain-release" of any audio to impact a portion of your sonic creation.