When you right click a DMX channel in QuickDMX you have an option to assign Sub master 1-8 to each channel.
It turns out these are not master faders from the live panel, they were implemented for a specific users project.
This is the explanation I got back from Pangolin support
DMX has 8 separate masters. Basically, simple multiplier (0..1).
It was made quickly for a large Client so they could set the master to any DMX channel.
The master (sub master) can be controlled via object tree.
Example of use:
DMXMasters.0.Value = 100
Set master to 100%
Example 2:
displaypopup dmxmasters.0.value
Show the value of master.
This is pure BEYOND, no relation to FB4, Just multiplier for DMX channels value.