Beginning to dive into FM-X a bit more, I thought I would start by trying to program up someone else's DX7 "voice" by following an Aftertouch Article June/July 1989 page 10 - reference http://yates.ca/dx7/AfterTouch-Magazine/AfterTouch-1989-06_07.pdf

Steps (For Nightshade):

1) I started with the FM-X init voice
2) Next I selected the algorithm. The article shows Alg 7 - but when I pick Alg 7 in Montage it doesn't match. I know Montage has 2 more operators - so it shouldn't match. But really Montage Alg 7 isn't anything like DX7 Alg 7. So I went in to search and chose the appropriate search parameters and didn't find anything close until I bumped up the carriers. Looks like Alg 29 is pretty close if I imagine carriers 1 and 2 are gone and imagine 3/4/5 switch places with 6/7/8. You'll have to excuse if it's obviously not correct - but this is where I maybe should do more research. At any rate, I pick Montage Alg. 29
3) Looking for ways to "disable" 1 and 2 - i find that if I do anything to "stop" carrier 1 - no sound comes out. Ok - for now I'll just ignore [1] and [2] carrier contributions and pretend like they're not there (for better or worse)
4) I see feedback is 3 - set that right on the Algorithm screen (0 -> 3)
5) Looking at the "PORTA MODE RETAIN" trying to set that up. Looks like the DX7 manual shows this as "P RETAIN" - so searching for that. Doesn't matter - since I notice time = 0 which disables the porta. effect - which is good because if this was going to do gliss - Montage doesn't support gliss that I'm aware of. I set time to 0
6) Pitch range - imagine that means pitch bend range because of the picture. range 7 and step 0. The range part I can set because 7 means PB- 7, PB+ 7 (the DX7 looks like the positive and negative bend cannot be different). So i set that up. One control difference is the step part. On the DX7, you could set the "gain" of the pitch wheel. The step is 0 = smooth - like what we have currently, while step = 7 would jump straight between no pitch and the maximum value since our range is 7. And if the step was 1 - we would hear the pitches going up by semitones with no between pitches. 2=whole tones, 3=so on... through max of 12. Not sure what happens when step>range - but I imagine it would just go up by 7 and limit the motion where the pitch wheel was changing pitches. Montage doesn't have this for values of 1-12 unless you setup "Pitch" as the destination and setup the curve to match - which is possible - just not "out of the box" easy.
7) Modwheel (mw), Foot Controller (fc), Breath Controller (bc), After touch (at) these have settings which I won't set right now. Aftertouch is disabled completely, so that's already done. Key mode Poly is already setup under the common settings
8) Next square - LFO
The DX7 has 6 LFO waveforms - so the picture of a funny step function is called "Sample and Hold" in the DX7 manual. Although - again this doesn't really matter since I see pitch and amplitude sensitivity (ams, pms) are set to 0. So I skip this other than making sure pitch/amplitude modulation are 0 for everything on montage - and I set the LFO speed to 0 for the heck of it.
9) Next square - Frequency/Output
a) I'm imagining pressing the operators 1-8 will let me edit. The numbers are not going to match the article since I have an extra 1 and 2 operator, so I'll start with what's in the article called "1" and maps to what's in the Alg 29 of Montage as "7" - so I click on "7" at the bottom of the screen which shows "Form/Freq"
b) The only "unclear" thing in this box in the article is "On/Off" - there's no element on/off - the only on/off in the DX7 manual is key on reset - so that's how I'll define this column. They're all "on" and that's the default for the init voice - so nothing to do there
c) "Level" touchscreen menu - I set the level for Op7 to 95
d) Same "Level" menu - I set "Level/Vel" to +4 to match the aftertouch article "vel sens" column
e) Back to "Form/Freq", I setup the "freq" column items. When there's an "x" under "mode" in the article, that's "Ratio" on Montage. A "Hz" in the article, and that's "Fixed". So I keep "Ratio" as default. And also Coarse=0 and Fine=0 results in a ratio of 0.50 which seems to match the article.
f) I set detune to -1, self explanatory.
a-f should repeat for the article operators 2-6. Just a repeat of the above with the next row of info filled in, and mapping:
Article Op 1 = Montage Op 7 (for reference below)
Article Op 2 = Montage Op 8
Article Op 3 = Montage Op 6
Article Op 4 = Montage Op 4
Article Op 5 = Montage Op 5
Article Op 6 = Montage Op 3

... by the time I setup the 6 operators it certainly sounds like something. on to the next part
10) Next square - Scaling
a) Referring to the above map - I'll start on the montage with op7 or article op1 and setup the scaling
b) Under scaling - I'm glad it shows "NORM" because I'm not sure what to do, right off, on the Montage if the scaling mode was Fractional - which I am guessing is the other value that could be here.
c) All the curves look like straight lines. So I'm calling the ones like "/" (ramping up) as montage +Linear and ramping down "" as montage -Linear. This is setup in the "Level" menu. For Op7 (=op1 in article), I setup montage "Curve Lo" as -Linear (default) "Curve Hi" as +Linear, "Lvl/Key Lo" as 20, "Lvl/Key Hi" as 18, and breakpoint is already C3 - so no change there.
d) Repeat a-c for the other Ops using the DX7 to Montage Op# translator for this alg. above

not a huge difference with these programmed in terms of overall character - but that's fine .. moving on

11) Next square - Envelope
a) Starting with Op7 again on Montage, same "Level" screen since it looks like attack/decay are here.
b) The Montage and DX7 are a little different here. DX7 uses starting level and rate and the numbers mean different things in R1 L1 (1 as the number) so let me see ...
R1 = Attack time
L1 = Attack level
R2 = Decay 1 time
L2 = Decay 1 level
R3 = Decay 2 time
L3 = Decay 2 level
R4 = Release time
L4 = Rel(Hold) level

On the same page (montage) the only other parameter is "Time/Key" which maps to "Rs" in the magazine article.
So following article Op1 (Montage Op7) - I set:
Attack time = 85, Attack level = 91, Decay 1 time = 35, Decay 1 level = 57, Decay 2 time = 0, Decay 2 level = 64, Release time = 25, Rel(Hold) level = 0, and Time/Key=2. I keep Hold Time = 0 since DX7 doesn't seem to have this.
c) wash and repeat for a-b for other ops.

12) after doing all that, I turned the level off (set to 0) for carriers 1 and 2 since now the other carriers have inputs - they're making sounds.

I'm guessing unless I made an entry mistake that I'm hearing how this voice is supposed to sound.

The notes say "The voice most resembles a combination plucked chime / bowed trombone sound". Well, I don't know what a bowed trombone is unless it's a present - and I'm not hearing high-frequency stuff I would expect from a "chime" kind of a sound. But maybe this is what was intended.

Maybe it's also documented somewhere else, but this can be used as a way to translate those aftertouch voices into montage FM-X. Well, unless there's LFO things or fractional scaling because this voice didn't have to cover that.