I have created a new performance as follows. Left part voice is choir+strings and right part is flute (mono). When I move the mod wheel to adjust the balance between choir and strings the flute voice also changes (vibrato is added). Is it possible to adjust the two parts of the keyboard independently?

If what you want to do is stop the MW from adding vibrato to the flute, that’s easy. You can use the MIDI Receive Switch to stop the MW data from affecting the Part that has the flute. See page 69 of the MOXF Reference Manual for details.

You may find that you would like to create custom Voices for your Performance. While in a Performance you can turn ON/OFF whether a particular Controller affects a Part using the PART parameter: RCV SWITCH, in order to change the Controller assignment itself, you must edit the actual VOICE back in Voice mode. STORE your new Voice to a USER location, then use it in building your Performance.

It’s possible to create a custom flute Voice that adds vibrato via AfterTouch (for example), instead of the MW, this way you can apply vibrato using a separate Control source. When creating a Performance some times it is necessary to also create a custom Voice that is prepared for just a particular combination (Performance).

This becomes necessary some times simply to create the controllers work for your particular playing preferences. Many times you will combine sounds only to discover the controller conflict… Especially when MW is involved. The MW is used so very often as a Pitch Modulation Depth control (vibrato), when you wish to use as a convenient level mix tool, you may need to adjust your controller setup. You can use the Part parameter RECEIVE SWITCH which saves a lot of work or you can plan ahead and customize the Voices themselves. Your choice.

As an alternative I your example, you could set the Choir/strings layer so that MW is switched OFF, and you control the balance between the two Element groups with the Assignable knobs (ASSIGN 1/ASSIGN 2) for example.

To Expand on Bad Mister comment....

Reprogram the choir+strings patch from using the MOD wheel to use expression.

That way you have vibrato for the flute on the MOD wheel and adjust the balance between choir and strings with expression.

Thank you all. You have solved my issue and opened new avenues.