1. Is there a way where I can load only the voices (and their associated waveform data) that I want?
As you know, there is no Voice mode in Montage. It has Compatibility with Motif XF Voices (which it loads as Single Part Performances), User Arpeggios, and Waveforms. It's writes the data in your .X3A or .X3V to 512 normal + 32 drum locations of the 640 Performance locations in the internal User area.
At all times, once a library is installed everything you need to make that Library play are available in the Montage.
But, no, to answer the question, it is not possible to selectively load data, it's a kind of "all data" import to internal User > then while in User memory, eliminate unnecessary data, then create the Library file and then finally, install that Library file.
Once a library is installed the User area is free to handle new data.
Remember in Montage a Library is not only the Waveforms and Samples but as many as 640 Performances that work with that data... Or that you care to keep with that data.
2. What difference does it make whether an .X3A file is loaded as a User file or Library file?
The Montage can import data from a Motif .X3A file, which it writes into the internal "User" area of Montage. You can then delete the items you don't wish to install to the Library file. You can also create new custom programs and add to the imported data. This customized "User" can then be written into the Read Only Memory area... you do so by using the SAVE option to write this User data as a Montage LIBRARY .X7L file. It is the .X7L file that then can be loaded/installed into a Montage (ROM) Library.
Only a Montage .X7L can write data to the Library area of Montage.
While your .X3A data is in "User" area, you can remove unwanted programs, create Live Sets - eight banks with 16 Pages each - 128 Live Set Pages made with this data. Once you have the data in USER exactly as you like it, then and only then do you Save as a "LIBRARY". Once you save the .X7L file immediately LOAD it to write it into semi-permanent Read Only Memory (Flash).
Each Library can include as many as 640 Performances and the Waveform and Arpeggios that make them work. Never again will Waveform and Samples be in memory without the programs that use them!
3. Some of the Motif XF files have the additional n-extension, e.g. .n2.X3A or .n3.X3A, where the n-extension refers to memory location in Motif XF. I assume the n-extension has no impact for the loading into Montage?
It does not. The .n1, .n2, .n3 designation was unique to the Motif XF's 2 slot system. Montage has been taught how to interpret this and it knows how to deal with the data.
4. I have loaded the full Bosendorfer.X7L file into the Montage and have now all 16 performances from this library available. In case I only wanted some of the performances from an .X7L file (like I only want some of the voices from an .X3A file above), is there a way to do this without keeping data in the Montage that is not needed?
In the case of the Bosendorfer Library it would make no difference. All the Performances made for the Library use the same Bosendorfer Waveform and Sample data. The locations that hold the Performances are there whether or not they contain meaningful data.
If a Library contains Waveform and Samples that you do not use, they should be removed prior to creating your XF file. I believe it is assumed that any data you backed in your XF was "meaningful" data. This way when the Montage imports your data it is exactly what you want to have in this Library.
Unlike the Motif XF or MOXF, when you load a Library file .X7L it places all the Waveforms and Samples plus all the programs that go with them (all 512 normal and 32 drum kits from the original .X3A file and potentially an additional 96 new Performances you create can using the Montage engine) and are in ROM (Read Onlt Memory). Basically, Libraries are your own personal customized "Presets", in that they will always be accessible.
The concept is put the programs you always want to have available in your Librariies... It really is like your own "Presets".
If ever you require to make a change to your Library, you can move it into USER, where you can make the changes, and then overwrite the data to update it.
If you wish to make a change to an installed Library you can move it back into User memory, make those changes and reinstall it, overwriting the previous install. We will have detailed guides coming in the Resources area.
We realize you are looking for a "load single" operation or a "load one bank", that's not available - it imports all voice, arp and waveform data in the XF file. It's best if it is organized prior to loading but you can manage what is in memory by moving data into "USER" where you work on it, create (save) a Library file, then install (load) that Library file.