Maybe this thread helps?

https://yamahasynth.com/forum/instrument-definition-for-montage#reply-20035

I'm not sure what your computer platform is. Also not sure if the Mac issues got ironed out if that's what you have.

Translation of the note still says:

find information on Patchmane xml format for Cubase directed by Tony Escueta for Yamaha Installation OS 1.10, beware that file can not be used with OS 1.50 / 1.51.

So I have a flagship Yamaha montage. And I also use Steinberg Cubase 9, which is owned by Yamaha. I like montage connect, but why is there no XML instrument definition for montage in cubase9?

Montage Connect was developed so that it can capture the current setup in the Montage and it automatically bundles it with Cubase Project memorizing every parameter in your setup.

The XML file only memorized the Factory Preset Performance locations. Given the nature of Performance creation the traditional XML listing is only useful for folks who use the Performance data unedited. The Montage Connect utility captures and keeps all of your edits which as you get to know Montage is bound to be apart of the workflow.

And because in order to use an XML, you would need to constant update it and/or restore the same Performance Parts to your User Bank for each and every Project. The Montage Connect is more efficient.

I have heard rumors that this was to come.
Anyone have an idea when?

Given the nature of the early XML files created and the discovery of how the User Bank is populated, I'm not sure when or even if an XML will be useful. You will need to determine that.

Here's why I say that... Montage Connect captures your current setup for the Project.
XML is a static listing of the Performance Banks that will depend on the same User Bank data occupies the instrument as when you saved the file. Montage Connect returns the data in the Performance at the time you were creating the Project...