Question: How can I clear (erase, initialize) the User Bank area?

Press [UTILITY]
Touch "Settings" in the first column and ""System" in the second column
Find the box that specifically says: "Initialize User Data"
This clears all data in the User Bank area of the instrument.

You can delete individual Performances by navigating to the "Performance" Folder.
Press [UTILITY]
Touch "Contents" > "Data Utility" > touch the Folder named "Performances"
the folders that appear under Data Utility represent you current user created data... Arps, Libraries, Live Set, MotionSeq, Performances, Songs, Waveforms

Touching the PERFORMANCE folder will list your current User Bank Performances. It will report how many out of 640 you have created thus far: "User Perform: xxx/640
A box for each Performance will be shown and if more than can fit the screen use the PAGE option in the lower right corner to advance.
You can opt to view your Performances alphabetically (or reversed), or by the order in which you added them (or reversed)... just touch the box "Name" or "Date" repeatedly to toggle the direction arrow.
If you select an item you will see an option pop-in window to RENAME or DELETE that item.
If you prefer to DELETE multiple selection -- you can tap the "JOB" box (turns green when active). This places a check Box in each item - you can now make multiple selections, one-by-one, or you can "Select All". A check mark appears and you can touch "Delete".

Also, I'm still not sure of the exact differences between Backup, User, and Library files.

The MODX comes with Factory (Preset) Performances, Waveforms, Arpeggios, Motion Sequences, Curves, Live Set, Quick Setup templates, etc. You, 'the user' get to create your own Performances (maximum of 640 of them), import your own custom Waveforms (maximum of 2048 of them), Arpeggios (256), Motion Sequences (256), Curves (32), Live Sets (8 Banks of 256 slots), etc. These are created and stored to the area of memory called the USER BANK. When you SAVE a USER FILE (.X8U) it saves all the custom Performances, Waveforms, Arpeggios, Motion Sequences, Curves, Live Sets, etc., etc, that you have created into that file.

If you were to SAVE that same data but set the SAVE CONTENT TYPE = LIBRARY FILE (.X8L) the MODX would be tasked with rewriting the data so that it is installed in your instrument ROM (Read Only Memory)... called a Library. The Library is a User Bank that has been 'cast in stone'. Basically, you are putting it in an area of memory that will always be there - until you either decide to delete or initialize the instrument

A BACKUP FILE (.X8A) is for archiving purposes - it captures everything in your instrument as one complete FILE. This is the ultimate SAFETY file - keep a copy in a safe place.

How you backup and which way is best depends on your goals. If your goal is to take a snapshot of your instrument to restore later exactly everything as it stands at the time of your backup - then using the X8A is best. X8A will save all libraries, user content, system settings, etc. Why not just use X8A all the time? Well, you may not want a snapshot. You may want to only restore partial information and keep some content in-tact on your MODX.

Say you have a collection of Libraries today - but maybe have a different combination down the road. Really what you want to backup are custom Performances you've accumulated in your user area. You want to be able to restore those later without upsetting whichever Libraries you may have installed in the future (which may be different). So saving a user file X8U makes sense here.

When you want to generate your own Library file to install a customized Library - you're going to want to create an X8L. I would suggest every time you generate an X8L to also generate an X8U. You can install ("load" ) an X8L - but you cannot directly edit it with MODX alone. You CAN, however, modify the X8U in the sense that it will load into your user area - you can make edits to the user area - then export a new X8L (and suggesting X8U again) file with your modifications.

Every single library you currently have installed in your MODX must have started as an X8L (or X7L) or some legacy keyboard's save file for conversion. What I'm getting at is that every single Library installed in your MODX has a file somewhere in your possession as the mechanism to land that Library to begin with. Therefore - it is not absolutely necessary to always save your Libraries. That said - if you have content referencing a Library - then the Library has to be re-installed (loaded) into the same slot. Something that can be difficult to manage. The backup (X8A) ensures all data is aligned. Misalignment can happen if you start deleting Library slots and slots become out of order after re-install. A good way to avoid this mess is to strive not to reference libraries if you can help it. Keep libraries self-contained. If you need a new Performance that references the library - backup your user area (X8U), then wipe your user area then import the Library you want to change to the user area, then delete the library just imported, then add your new Performance which references content in the library (however, now in the user area - so it will reference the user area), then create a new X8L (Library) and X8U file, then reload (install) the new Library file you just created. It will have the new Performance which is inside the Library and only references itself. Your user area will not reference the Library area.

NOTE: The above step to import the Library to the user area is not necessary if you previously have an X8U version of the Library. You can skip the import and skip initializing the user area. You can simply load the X8U into the user area which will overwrite your user data and also place the same content that was previously installed as a library to the user area.

Very good. Thanks. I'll do some experimenting to make sure I understand this stuff.