Hello. Google this: "yamaha montage data list"
Sincerely
D

I usually search for "yamaha montage downloads" to land on the right page. Here, you will find all of the manuals. You're going to want to have the latest of each manual downloaded for reference as searching the PDF can be easier than thumbing through a paper doc. Or you can print them out if you really want to do that.

For the US - the link is currently:
https://usa.yamaha.com/products/music_production/synthesizers/montage/downloads.html

... which brings you to the downloads.

Under "Manuals" you'll see:
MONTAGE6/7/8 Data List for V3.50 (this is currently the latest - you can ignore the other docs for earlier versions)
MONTAGE 6/7/8 Owner's Manual
MONTAGE 6/7/8 Supplementary Manual (hopefully latest - you can pull the latest from your firmware update zip)
MONTAGE6/7/8 Reference Manual
Synthesizer Parameter Manual

Note that when you download firmware updates - there's also a collection of updated docs inside the firmware ZIP file. Most importantly from that collection is the "Supplementary Manual" which contains all of the updates to manuals for new features presented by the firmware updates dating back to very early firmware updates to the latest.

The Data List has lists and tables (factory preset Performances, Arpeggio list, Waveform/Sample list, Effects list and parameters, MIDI implementation and sysex registers, etc). It's sort of the most detailed lowest-level documentation.

Going up from there is the Reference Manual. This is a complete end-to-end description of all of the features of Montage. It walks you through all of the menus and settings with descriptions of what they do. This is the most detailed "how to use Montage" manual.

Going up from there is the Owner's Manual. This is a high level description of how to do some basic things with Montage. It also sets the foundation of standard names for buttons and such. In the beginning, a good route to take is to look in the owner's manual first for answers - then drill down to more detailed docs (one by one) if you do not find what you're looking for.

The Synthesizer Parameter Manual is sort of a glossary specific to Montage. It will show different concepts of effects, envelopes, etc. with pictures (and description) in order to define the Yamaha way of implementing various things. It's not quite as detailed as the Data List in terms of specific implementation - but pretty close for some items. I rarely refer to this manual - but it is good information for those few times when the others fail to convey the needed detail.

You'll want to become familiar with each doc type so you can most quickly grab the right one for what you're looking for.