I realized that I wrote a badly question.
Answer is: upload/save file in .x6s (All song)
3 band, 3 file .x6s.
My doubt, however, is always better to load the .X6A file?
Some settings or parameter are not lost?

The .X6S file includes All Song data... this includes the 64 Song locations, and any MIX VOICE data stored locally to a Song. It does not include any User Voice data not stored locally within Song as a Mix Voice. Nor does it save any Patterns, Master setups, Utility setting, etc.. only data related to the Song Sequencer.

The .X6A fill includes All data, including all Songs, Patterns, Mix Voices, User Voices, User Arpeggios, Master Mode, Utility settings, and will include any User Waveforms. All data saves Everything!

I'd recommend to have one ALL file with included user waveforms as Backup of the flash module and the other ALL files without user waveforms. Loading an ALL file with waveforms can easily take an hour with a good filled 1024MB module while loading an ALL file without the waveforms will take only a minute. You also don't have to load everything from the ALL file. If you want, you can load only the songs or only one song from it. If you don't make edits on your user voices which you are using in your songs or if you're using only the preset voices, it should be safe to store just the X6S files which are smaller and save and load even faster.
Here is what I did:
I loaded the Inspiration in a Flash Library bankwise and then selected the sounds I want to keep and initialized the others to free up the user voices. Then I reaaranged the locations of the user voices to have parts of USR2 and USR3 free for my other or my own voices. Then I deleted all unused waveforms I didn't want to keep. (you can see if a waveform is used by any voice in the waveform list). Then I did the same with other sound libraries I use.
When I was finished, I saved an ALL file with waveforms as full backup of everything including the contents of the flash module.
Now, when I'm editing voices I save either ALL files without waveforms or just voice files. When I make a song or pattern with that voices I just save the song/pattern data. But it's okay to save them as ALL files as well as all songs and patterns are included there. I treat the flash module like a second waverom. As long as I dont't alter its contents it's not necessary to save them every time. When I add or delete waveforms i update my fullbackup.

Btw. you can save a voice file with waveforms which saves only the waveforms which are actually used by a user voice. If you then reformat the flash module and load the file back in, you have your waveforms nicely in order without unused slots in between but you should be aware that this procedure takes some time.