Is there an equivalent of a Dual button function, as there is on my old PSR-530? Say, if you're playing split keyboard with organ-A on the left, a bit louder lead organ-B on the right, can you select (somethin) and add, say, horns to organ-B?

The MX is very different from your old PSR-530. While some things will be similar, the design concept is quite different. There are no Styles or Fill-ins or auto-accompaniment like on a PSR.

Yes, you can play a "Single" sound, press the "LAYER" button to play what you call "Dual", or you can hit the "SPLIT" button which will play one sound in the right hand and another sound in the left. But to add any addition sounds to play "live" you will need the VycroMX Performance (free) Editor.

I read some place about a method of creating more than one split point by using vycroMx and setting voice ranges... maybe? If so, the free or Pro version?

Both Editors will allow you to accomplish this. And Edits you do with the Editor can be stored in your MX's internal memory.

Can you plug a momentary off/on (Radio Shack-type) pushbutton into the Foot Controller jack, and then assign the mod wheel to it to ramp the organ rotary up/down? If not, what model footswitch would be required to do that?

Sadly, Radio Shack is out of business. A momentary switch can be plugged into the MX and is globally assignable. You also have an option for a sweep type pedal.

Yamaha recommends the Yamaha FC3, FC4 or FC5 for momentary foot switch duties and the Yamaha FC7 for sweep functions (volume, filter, modulation).
Either type of pedal can be used to flip the Rotary Speaker effect from Slow to Fast and vice versa.

Most folks use the Foot Switch for Sustain Pedal duties and use the Foot Controller jack for all other functions. But it is up to you.

For more information about (free) VycroMX Performance Editor

Thanks, Bad Mister, was hoping to hear from you while I still had the MX out on trial. And 10-4 on Radio Shack – just an example. I have a momentary off/on switch I used on my Alesis QS6.2 to control rotary, but couldn't make it have any effect on the MX. Maybe you can tell me how to assign my switch and I'll try it in the am... getting kind of late for Ol' Will here. I also have the free version VycroMX Performance Editor loaded up, but will work with the manual a bit before asking any how-to on the other stuff. Thanks again!

Plug the FS into the jack marked Sustain
Press [UTILITY]
Use the UP/DOWN CURSOR to advance to 03: Controller
Again use the UP/DOWN CURSOR to find FS
Set the FS = 01[Mod Wheel]

The Foot Switch will now act like the Modulation Wheel. Being a momentary off/on, it will work like a sustain pedal: you will need to keep your foot on it to switch to the other speed. For example the ORGAN VOICE "16+8+5&1/3" starts in the SLOW speed setting, when you want FAST hold the pedal down. The Rotary Speaker speed will transition from SLOW-to-FAST as programmed within the Effect. You can program the Rotary Speaker Transition Time separately for the Low Frequency Rotor and the High Frequency Horn from the MX's front panel. (Editing the INSERTION EFFECT is a function in EDIT > PART > 05: VOICE INS EFF)* It will take a minute of two with the Manual to translate all the abbreviations, but you can completely edit the Rotary Speaker Effect to suit your need.

The difference between the MW and the FS is that the MW can remain in the UP or DOWN position without you having to 'hold' it in place. It works more like the standard Chorale/Tremolo switch on a Leslie. But if you want to use the FS you can, as long as you don't mind "working" the pedal like a sustain pedal (holding it in place). Also you give up your Sustain pedal function.

Another option would be to use the FC7 sweep type pedal (as I mentioned). It like the MW will remain in the UP or DOWN position without you having to 'hold' it in place.

Okay, I got the mod wheel assigned to the Sustain input, and all works as expected in that regard, thanks. Only I don't want to give up sustain, so I was hoping to make my momentary switch work in the Foot Controller input, rather than the Sustain input.

I tried plugging my sustain pedal (Yamaha model 3805) into the rear FC input and changing Utility | 03:Controller | FC1 and FC2 (independently, then both) to Mod Wheel, but got no rotary change when pressing the pedal. Again, the "pedal" I want to use in the FC input is really nothing more than light switch. If that will work, its only purpose will be for the Mod Wheel, and having to hold it down is perfect for the way I use a Leslie. Just need to know how to set the 03:Controller values -- thanks!

PS: I also have an old round Yamaha PSR Pedal-2 (that works in reverse when plugged into the Sustain input) just in case that might work...

Yamaha recommends the Yamaha FC3, FC4 or FC5 for momentary Foot Switch (FS) duties and the Yamaha FC7 for sweep functions (volume, filter, modulation) Foot Controller duties.
The pedals you mention are for PSR keyboards - which is a whole separate wing of the huge company that is Yamaha.

Just FYI, the FC (Foot Controller jack) works with a TRS (Tip-Ring-Sleeve) type 1/4" connector. And is an assignable jack. While you cannot cause harm by plugging in a non-recommended pedal you will not in all likelihood get near the proper response.

The FS (Foot Switch) will either work correctly or in reverse due to polarity (TS connector Tip-Sleeve). SO you have a 50/50 chance with any odd Foot Switch. But since the FC (Foot Controller) has definite tolerances that must be met, you are best getting what Yamaha recommends for the task.

The PSR/MX delineation is totally understandable. To me, the MX learning curve seems to be more like what I experienced with my Alesis QS6.2. It took a lot of digging and trials to get it set up like I wanted, and I'm prepared to spend some time learning the MX. Just hoped to re-purpose some pedals if I could, as I've fabricated my PK5A bass pedals platform for potability and quick setup.

Appreciate the TRS info on the pedal wiring; it led me to try a couple of things with the FC input, but haven't cracked that nut yet. I did slip by the music store and borrow an FC3 pedal to try. I set and stored Controller:03 FC1 to Mod Wheel, but when the FC3 is plugged in the rear FC input, the pedal works in reverse; ie, the organ is ramped up until I press and hold the FC3. Not surprising, but just don't know how/where to switch the polarity, as I don't see a physical switch on the pedal, and neither the "turn off MX, plug in pedal, turn on" nor "press pedal, turn on" routines did any magic...?

Bad Mister, I think I misinterpreted your reply about the footswitches, assuming I could use any one of the FC models in the Foot Controller input. I see the op manual specifies FC7 for that input, which probably explains why the polarity is reversed when I plug in the FC3. I really don't have space for an FC7, given the tight layout of my homemade bass pedals platform, so now I'm trying to fabricate a TRS pushbutton style "pedal" dedicated to rotary -- which I know is outside the scope of this forum. Thanks so much for your help on this one.

Just to confirm, in case anyone else is interested, I was able to try an FC7 pedal in the Foot Controller input, and it indeed ramps the rotary up/down, as expected (when Utility | Controller 03: FC1 = Mod Wheel). Unfortunately, that size pedal is not an option for me, but I may have a workaround... Where there's an Ol' Will there's a way 😉

And there was a way... With a 50k ohm linear pot and some odds and ends, I now have a foot-operated mod wheel, as well as a rather crude sustain "pedal" made from a door bell. Can supply specifics, if anyone's interested...