As far as the MOXF6/MOXF8 Editor Standalone/VST is concerned... whether or not a VOICE that appears in the EDITOR can be heard depends on whether or not the Status of the EDITOR is ONLINE or OFFLINE.

When ONLINE appears what you see in the Editor is what you will hear in the MOXF.
When OFFLINE appears what you see in the Editor can be quite different from what is sounding in the MOXF.

ONLINE means the MOXF and the Editor are on a 1:1 relationship. And what one shows the other shows.
OFFLINE means means they are not together... what appears in the Editor can be different from what you hear when you play the instrument

It is not clear from your question what you are doing in VOICE mode with Cubase? You can have Cubase recall all the sounds you used for each Project. This can include all USER 1, USER 2, USER 3, USER DRUM, and 16 MIXING VOICES... in addition to the current MIXING setup of 16 PARTS, and all your global (Utility mode) settings. You can have the Editor automatically restore all of these or some of these when you first open the Project File.

MOXF6/MOXF8 Editor VST

I didn't express myself clearly.
When I rehearsed with my band I created some user voices. Now we are recording a CD and I have to use those voices inside a cubase project.

VST editor in online in song mode. For channel 1 it recalls the USER VOICE 1 - 010 but that's only written, when I play the file I don't get the sound I've created but the default sound located in that memory (Monkey Bars). When I re-select the voice (by rechoicing and double-clicking on the voices' list) I finally get the sound I've created.

To be clearer let's start from a Factory Reset on the keyboard and a new Cubase Project.
I prepare a customized voice, stored on US1 001 (by default in that location there is the sound called Everlasting Glory, a pad). Now I initialize this voice and I create a simple new one, with just a sine wave (waveform 1388) on element one and store this voice like SimpleSine on the keyboard at USER1 - 001.

Now I open Cubase, chose the template that prepares 16 channels and links them to the VST editor.
Now VST editor is online in Mixing mode, on the keyboard there is the song mode ("01: Dusk2Dawn" appear on the display; now I press "DawRemote" on the keyboard and I get my Remote Control Screen on the keyboard).
I set the VST Play mode (Quick Setup 6)

I get the piano sound on channel one (PR1 001) Full Concert Grand

Now I click "Full Concert Grand" and on the right appears the list ov voices to chose from. I change the voice. I chose the one on USER1 001: I find it called still "Everlasting glory" but it sounds like the one I've created (the sine wave). I chose it by doubleckick on it.
I save the Cubase project and I close it.
I re-open it; VST Editor and MOXF6 are syncronizing....

Here is the problem: on the VST Editor (that now is online in song mode) on the first channel I find the voice USER1 -001 "Everlasting Glory" and the problem is that sound just like the original "Everlasting glory" (I get the sound of the original pad located in that memory place USER1 001 after the Factory reset).
I click on "Everlasting glory", on the right side of the VST window appears the list of voices I can chose from.
I simply double click on "Everlasting glory" and...da da! It sounds like my edited sound Simple Sine! (despite it's still called "Everlasting glory" both on the voices' list and on the channel one voice name).

What am I mistaking? I'd like to close and open a Cubase project finding exactly what I had when I saved it, otherwise I have to re-choice every single voice at every project's opening.
I hope I've been clearer than before.
Thank you for your patience.
Luigi.

Hi Luigi... You are missing an important step. The MOXF Editor VST does not "know" what is in your hardware MOXF until you BULK that data into the EDITOR. We'll outline what you need to do. You did not mention which version of Cubase you are using so we cannot put in any helpful screenshots. But they all pretty much work the same:

In order for the EDITOR to "know" what you have in your internal MOXF you must IMPORT the current MOXF Library into the EDITOR. No where in your description did you do that.

Here's a correction on what you wrote:..............................

Let's start from a Factory Reset on the keyboard and a new Cubase Project.
I prepare a customized voice, stored on US1 001 (by default in that location there WAS the sound called Everlasting Glory, a pad). I initialized this voice location and I created a simple new one, with just a sine wave (waveform 1388) on Element one and store this voice and I named it "SimpleSine" USER1: 001(A01).

Here's where you go tragically wrong...............................

Now I open Cubase, chose the template that prepares 16 channels and links them to the VST editor.
Now VST editor is online in Mixing mode, on the keyboard there is the song mode ("01: Dusk2Dawn" appear on the display; now I press "DawRemote" on the keyboard and I get my Remote Control Screen on the keyboard).
I set the VST Play mode (Quick Setup 6)

........................................................................................

_ First, using a TEMPLATE does not necessarily help you in what you want to do... Let's learn how to set it up manually (by hand).
_ Second, the DAW REMOTE mode is to control Cubase, has nothing to do with getting your sounds into the Editor. It has nothing to do with the Editor, at all. You use it to START/STOP Cubase, and stuff like that... not necessary, quite yet.

What you should have done here is:
1) Open Cubase to an EMPTY TEMPLATE found under the heading "More"... first because you don't know yet exactly what you are going to do. I do not recommend the Templates until you are certain of what you are doing and certain that the template serves exactly that need. Plus it skips ahead _ when you want to LEARN something, I find it helps to set it up manually first. Then you know what is going on and what you need to do. If you open a template -every thing is done as the author of that template likes to work. What if it is NOT how YOU like to work. Skip the Templates for now. LEARN how to setup the MOXF as a VST manually! Trust me!

2) Clear all the SONGS and PATTERNS in your MOXF. You are getting ready to make YOUR music _ get that stuff out of your MOXF. You are not going to need it. Here's how:
Go to SONG mode > Press [JOB] > Press [F6] SONG > Select CLEAR SONG > Set the SONG NUMBER = ALL > Press [ENTER] to execute
Go to PATTERN mode > Press [JOB] > Press [F6] PATTERN > Select CLEAR PATTERN > Set PATTERN NUMBER = ALL, Set SECTION = ALL > Press [ENTER] to execute

3) Call up a blank MOXF SONG (or PATTERN) location - it will not matter which... for example, call up blank SONG 01

Next we will launch the MOXF VST EDITOR inside of Cubase and then "teach" the EDITOR what's in your MOXF: Here's how:
In Cubase, go to DEVICES > VST INSTRUMENTS > RACK INSTRUMENTS > EXTERNAL > MOXF VST

This will create the VST INSTRUMENT Folder with the MOXF VST SubFolder, an AUTOMATION LANE, a virtual AUDIO LANE, and you will be asked to create a MIDI Track for this plug-in > Click OK to create it.

This is the first MIDI Track - it is assigned so that MIDI OUT is routed to the "MOXF6/MOF8 VST - Midi In" and is routed on MIDI Channel 1
You will create a new MIDI Track for each PART you want to record in Cubase, when you need them. Each will be assigned MIDI OUT = "MOXF6/MOXF8 VST - Midi In... and the channel number will automatically increment 2, 3, 4 and so on.

The MOXF EDITOR VST window will open.
IMPORTANT: Import your current MOXF Voice Library into the EDITOR, here's how:

Click on "BULK" on the Editor's menu bar
Select DATA SYNC
Set the dialog box so RECEIVE data from the MOXF (arrow points from keyboard to computer) - you want to capture the USER 1, USER 2, USER 3 and DRUM USER banks.... YOU have only changed USER 1:001(A01) but you can understand that this is how you move Voice data from the hardware into the software.

Now the Editor is synchronized with the VOICES in your actual MOXF. Until you do this the Editor opens with the default Voice set that comes in a brand new MOXF... not YOUR MOXF's current library. Now if you bring the EDITOR ONLINE...

The EDITOR will have the VOICES that are in your MOXF. When you select USER 1: 001(A01) it will be "SimpleSine", not "Everlasting Glory"

By BULK RECEIVING into the Editor your internal library, when you next open Cubase the Editor will restore all your sounds (well, actually you can select to have it restore just the 16 VOICES you used for the SONG, or you can have it restore all 384 Normal and 32 Drum Kits to your MOXF). You determine what the EDITOR will do by how you setup the AUTO SYNC SETTINGS parameter on the EDITOR's SETUP screen

This is covered in detail in the following tutorial here on Yamaha Synth:
MOXF6/MOXF8 Editor VST

Clear as always. I hope this can be useful also to someone else. Next time I'll double check all the manuals and resources on this site before posting a new topic. Once more thanks a lot