Sliders will send CC7 if you press [PERFORMANCE] (HOME) to ensure no Part is selected and also have not disabled the sliders.

Local control is turned off in Zone master

Are you sure? Because there is no "Local Control" setting in the same screen as any Zone setting. The Part Settings->Zone Settings menu has something called "Int SW" which is different than "Local Control". And "Local Control" is a "MIDI I/O" setting not associated with Zones.

I'm just making sure I'm following your setup correctly.

Because you have setup Part slot #8 to communicate with your external device. You call it Local Off - while we understand what you mean, technically you probably mean the “Int Sw” = Off so only your external synth is controlled by this Part slot, via the Zone Settings.

You seem to also indicate that you have turned Off the Bank Select and Program Change options.
However, if you leave the “Vol/Exp” option On, you can set a preset Volume for the external device.

By setting up the Part slot #8 as an external Zone, Slider #8 will control the Volume (CC7) of your external device… provided “Vol/Exp” is On.

The MODX has 16 Sliders for PARTs; they are setup in four sets of four, 1-4, 5-8, 9-12, and 13-16.
To the left of the Sliders you have a button that selects either “PART” or “ELEMENT/OPERATOR”

When “PART” is lit, you have 16 sliders one per Part.
The button directly under the Part button toggles “1-4/5-8” (use [SHIFT] + the button to jump to “9-12/13-16” )

So by tapping that [1-4/5-8] button once you will select Sliders 5-8.
Slider #8 controls the Volume of your external Zone when you are HOME

Alternate Methods:
When on your Zone Setting screen for Part slot 8, set the “MIDI SEND” option On (green), the Volume setting on this screen is now “live” you can move it and your external device will respond (CC7)

When/if you have an FC7 Pedal you can use it to control the Volume or Expression of your *selected* Part slot.

Did you know?
__if you are on the HOME screen and *select* Part 8, you can Exchange it with another Part slot.
Press [SHIFT] + [EDIT]
Select “Exchange”
You can now swap your Part 8 setup with any other Part

Thanks guys. Sorry, yes i meant “Int Sw” = Off.

Ive got it all working ok, as above, but thanks for the detailed exploitation.

What im trying to figure out is, based on the above, if part 8 has a volume of 100 set in Zone master, can i have another part with identical settings, but volume at 70, and switch between the two parts and have the volume change on the ipad?

For example. I have part 8 at volume 100 for when im playing just the organ (on the ipad), and have that as scene 1. On scene 2 id like a split, with Piano on the left and organ on the right, but with the organ at volume 70. Ive set this all up, but the volume doesn't change between the two scenes. So im guessing the volume CC7 is only sent once, when the Performance is first called up?
Switching between performances works ok, i have different volumes set up on part 8 in different performances. I always use part 8, just to make it easier to program.

Im not really looking for a workaround if the above isnt possible. As the iPad is coming back in via USB i just use the USB volume knob to control the volume of the ipad, but was just wondering if the above will work for the rare occasions i need to drop the volume quickly. I find this less confusing than using the sliders, as i dont need to make sure anything is selected etc.

I hope that's clear.

What im trying to figure out is, based on the above, if part 8 has a volume of 100 set in Zone master, can i have another part with identical settings, but volume at 70, and switch between the two parts and have the volume change on the ipad?

No, switching selected Parts within the same Performance does not reSend a Volume message via the Zone Settings. Recalling a Performance ‘sends’ all of the Zone Settings from all of the Parts simultaneously.

Switching “Scenes” can be used to ‘send’ a new Volume message (without engaging a second Part).
Set Scene 1 Volume = 100
Set Scene 2 Volume = 70

Here’s how:
From the HOME screen touch “Scene”
Across the top of screen are the 8 Scenes
Scene 1 is selected - bright blue
Turn On the MEMORY Switch for “Mixing”
Touch “Mixing 1”
Tap the screen area with the Slider — set Scene 1 = 100
Touch “Scene 2” along the top of the screen - turns bright blue
Turn On the MEMORY Switch for “Mixing”
Tap the screen area with the Slider — set Scene 2 = 70

Editing the Scene from this screen automatically Stores the Scene.
Now when you recall your Performance, the front panel Scene buttons will allow you access via the blue [SCENE] buttons.

When you [STORE] your Performance make sure that SCENE 1 is selected, if that is how you want to begin… Volume = 100.

The Scene buttons can also determine which of your Parts 1-8 are KBD CTRL active at the moment.

Sorry for the delay. i can only log in when im using a computer, not my iOS devices (still).

Thank you for the explanation. Just to be clear, the above set is for the internal sounds, not my ipad?
I tired it and can see the volume levels change on the MODX when i change the scenes (i use this a lot with the internal sounds already), but they dont change anything on the ipad or send a lower volume signal.

Sorry for the delay. i can only log in when im using a computer, not my iOS devices (still).

Thank you for the explanation. Just to be clear, the above set is for the internal sounds, not my ipad?
I tired it and can see the volume levels change on the MODX when i change the scenes (i use this a lot with the internal sounds already), but they dont change anything on the ipad or send a lower volume signal.

You are correct. The Scenes will memorize the internal Part’s Slider Volume levels, not the external devices level… when that external device is returning via USB.

But that said, the physical Slider itself, assigned as your external Zone will be real time access to your iPad volume whenever the Sliders are set to do Part Volumes. Sorry for the miscommunication. (I think this why I added the “did you know…” item… you can swap slots for your external device… this allows to place that real-time Part slider wherever you like.

If you use the KBD CTRL On/Off Scene Memory function, you can have a Scene that does not communicate with your external device.
One Scene is set to play both internal and the external slots, the second Scene is set control just the internal slots. Once you switch Scenes, all subsequent notes will trigger the KBD CTRL active slots.

The other option is to activate Bank Select/Program Change and have the external device control and recall its own Volume settings (this may or may not be possible depending on the iPad synth’s capabilities.