Simply make sure your firmware is up-to-date.
MONTAGE 3.51
MODX 2.52

The MONTAGE can read your MODX .X8U USER files, and your MODX .X8L LIBRARY files
And your MODX can read your MONTAGE .X7U USER files, and your MONTAGE .X7L LIBRARY files

So all you need is a USB stick. Save your MONTAGE User Bank to the USB stick, and then load it to your MODX.
The Library files can be loaded to either synth. (“Backup” file formats .X_A are not compatible)

All 2,227 MODX Presets are already included in the 2,739 MONTAGE Presets
If you add the 512 “Motif XF Performances for MONTAGE” to your MODX, They will have the same 2,739 Factory Performances. Free download at the bottom of the page:
Link — https://usa.yamaha.com/products/music_production/synthesizers/modx/downloads.html#product-tabs