I just purchased an MOXF6. Yay me!
And I am a MIDI novice. Boo me!
I have created a Master on the MOXF6 which consists of the internal tone wheel organ voice "16 + 8 + 5 1/3" [PRE1:083 (F03)] AND a tone wheel organ voice from an external device.
How can I route the external voice through the MOXF6 effects/modulation wheel, so that the MOXF6 controls the rotary speaker effect for both the internal and external tone wheel organ voices?
The external voice is sounding together with the MOXF6 voice when I physically play on the MOXF6 so MIDI connections are correct. But only the MOXF6 voice is currently affected by moving the MW (switching rotary speaker effect from SLOW to FAST).
Is it possible to have both the internal and external voices controlled by MOXF6 in this way?
If so, how?

Only the MOXF is going through the Moxf's Rotary Speaker Effect. You do not mention what the external device is, whether or not it has its own effects, so we cannot know exactly what moving the MW of the MOXF does to this unnamed external device.

You can route the external Synth through the MOXF Effects by connecting the outputs of that device to the A/D audio inputs on the back panel. This will give it its own audio channel and its own dual Insertion Effects in the MOXF. But there may be no need to do this if it has its own effects. But even if you do, real time control will be independent.

Thanks for your reply!
I am using a Roland RD-2000 as the external device. It does have its own Rotary speaker effect and I am looking for a way to trigger the effects on both devices at the same time with one motion, rather than trying to flip two separate MW's at the same time - not practical for live performance.
I have just tried a latching footswitch (Neewer NW-201) connected to both the MOXF6 and the RD-2000 via a mono y-adaptor and two 1/4" mono cables out of the footswitch, to control the SLOW/FAST rotary speaker effect of both devices, but this does not seem to work. Nothing is triggered. Maybe it's a faulty footswitch? Or type of footswitch (latching vs momentary)? I am assuming a latch-type footswitch (ON/OFF) will control this type of effect but am I wrong?
An old Yamaha sustain pedal (momentary switch) I had lying around works to trigger the effect when plugged in to the assignable footswitch input of the MOXF6, and then assigned to control MW in the Utility screen. However, I have to keep the pedal depressed to get the FAST rotary speaker speed (the way a momentary switch works) - but this is not practical for live performance.
I can try your suggestion to route the RD-2000 through the A/D audio inputs on the MOXF6 but was hoping to avoid doing that if possible.
Thoughts?
Ideas?

A clickable FS should work... try it on the MOXF alone.
Set FS = 01[Mod Wheel]
It will work, leaving your y-adapter in question.
Let us know...

I have tried the Neewer footswitch (mentioned above) with the MOXF6 and the Roland RD2000 each separately but it does not trigger the rotary speaker speed change on either device. A Zoom footswitch (momentary switch) triggers the rotary speaker speed change on the Roland RD2000 by pressing it and releasing it. Pressing it and releasing it again changes the speed back on the Roland. This is exactly what I want to do with both devices simultaneously. However, when I connect the same Zoom footswitch to the MOXF6, the rotary speaker speed change occurs when I press and hold the pedal, and the speed changes back when I release the pedal - not ideal - and now makes it quite confusing to physically synchronize the rotary speaker speed change of both devices. I guess I will just have to try a few different clickable footswitches to see if I can find one that will trigger rotary speaker speed change the same way with both devices....ugh....
Any further thoughts or suggestions?