It's no MIDI trick it's pure magic. 😉 You can select "part control" and play any of the 16 parts without interruption between parts while switching between them. I think one options is if you need some additional parts above the basic 8 for a solo for example. You'd stay in "performance control" for the main portion of the song using all of the advantages of keyboard control. Then comes a solo part that requires one of those parts 9-16. You'd switch over to "part control" and select your required part and play it. You'd have to experiment with how the sounds might be interrupted performing such a maneuver and then back again into performance control.

From what I've read around here, Performance Parts 1-8 can be played directly via Keyboard Control, and Parts 9-16 can be individually played from the keyboard when they are manually selected.

Apart from doing clever tricks with MIDI cables (like I read in another thread), is what I said above the complete story? I just want to make sure that I'm not missing some other straightforward way that Parts 9-16 can be useful.

You owned a Motif XF so let's for a moment use that so you understand clearly what's going on. The Montage is 16 Part multi timbral, like the Motif XF.
A 16 Part Montage Performance is the equivalent of the XF's SONG/PATTERN MIXING.

In the Motif XF, say you were in Performance mode, (remember?) you could play four Parts simultaneously - and from the XF Performance mode you could direct Performance Record those four Parts to the first four Parts of either a Song or a Pattern MIXING setup. When you finished recording, the four Parts of the XF Performance were copied to Parts 1-4 of the MIXING. Once the direct Performance Record was complete, you went to the targeted mode (Song or
Pattern) and could add data to tracks 5-16, using Parts 5-16... One at a time.

In the Montage you can play as many as eight Parts simultaneously (KBD CTRL) - you can record them as you could the four Parts in the XF Performance. This leaves Part 9-16 to add data one Part at a time.

If your Montage KBD CTRL Performance is just a single Part, it is like working with all single Parts in an XF Mixing.
If your Montage KBD CTRL Performance is two Parts then Parts 3-16 are available as single Parts. Overdubbing each one at a time.
If your Montage KBD CTRL Performance is three Parts then Parts 4-16 are available as single Parts. And so on.

EXAMPLE: If you remember the XF PERFORMANCE "Bop til you Drop"... It was four Parts: drums, acoustic bass, jazz guitar (under arpeggio control) and an acoustic piano. You can actually build this Performance in Montage... Say you do build this Performance in Montage with just these four Parts under KBD CTRL, and you set a Mute Trumpet in Part 5, a Soprano Sax in Part 6, a Concert Flute in Part 7, a Vibraphone in Part 8, a Jazz Guitar in Part 9, a Trombone in Part 10, a Tenor Sax in Part 11... Etc.

First you lay down about twenty choruses of "Bop til you Drop" doing a fast jazz blues, just comping on the piano throughout. Next, you go back (rewind to the top), select Part 5 (Mute Trumpet) you do so by pressing [PART CONTROL] > then [PART SELECT 5]. Now while listening to the "Bop til you Drop" playback you can Overdub a chorus of Mute Trumpet, at the end of a chorus or two, you can press [PART SELECT 6] and lay down a few choruses of Soprano Sax, and so on. No need to stop just switch Parts...

The Voice mode is no more, the Mixing mode is no more, they both are simply Montage PERFORMANCE mode, only now you can create what used to be called a separate mode (PERFORMANCE) in the XF, by activating KBD CTRL on any the first 1-8 Parts.

This weekend I'll post "Bop til you drop" with a setup of instruments so you can try it out...

I'm looking forward to "Bop..."

This may not be a practical thought, but it might be educational. I was thinking about how to use Parts 9-16 without having to individually select them.

Thinking about background parts like drums and bass, it occurred to me that if those parts were "Arp On" and "Arp Only," I might be able to "trigger" them from Cubase by sending them a MIDI "Note On" message. I could have a Trigger track in Cubase containing the "Note On" messages for however many of these channels I wanted to have playing backup. (Would I also need to send a "Note Off" message to each of these channels?)

This way, I could use Parts 1-8 for different solos.

I'm curious what you think about this idea, and also whether there might be other ways to "trigger" a Part like this in positions 9-16.

One other question: is it true for all 16 Parts that they receive MIDI on the channel that's equivalent to their Part number? In other words, Part 1 receives on channel 1, part 2 receives on channel 2, etc. I saw some threads around here that seemed to be saying that this is how it works, and that there is no way to change it. That's fine with me, but I'd just like to verify that it is in fact the case.

Thanks for bumping this thread, I completed the conversion of "Bop til you Drop" (I had about a half dozen requests for it) but I totally forgot to post it up here on YamahaSynth. I'll be flying home early tomorrow and will endeavor to get it posted either tomorrow night or on Saturday... with different ways to use it.

Find attached a small file containing just two Performance Examples: "Bop til U Drop(2).zip"
Please unzip the contents to a USB stick you use with your Montage

Make a backup USER FILE of your current Montage BEFORE loading this USER FILE (as loading this will overwrite your USER bank).

To find the two PERFORMANCES
From the HOME screen:
Press [CATEGORY SEARCH]
Set the BANK = USER
Set Category = ALL
There will be only two Performances in your USER area:

_ Bop 'til you Drop = the Performance as made popular in the Motif XF (I split the Arp Note Limits and Part Note Limits at C3, change to your liking).
You can change through five arp phrase sections using either the blue SCENE buttons 1-5 (left side), or the ARP SELECT buttons 1-5(right side). Change tempo to suit your liking.
Drums trigger when you hit a key below C3
Bass and Guitar comping follows chord voicing in your left-hand
Piano is "live" above C3 for real time comping or playing.

_ Bop 'til You Drop + = the same Performance except this time I placed eight instruments in the PARTs 9-16 for soloing -

As an example of how you can use the MULTI-PART (KBD CTRL) to lay down the music backing tracks, then overdub melody ideas or solos in a second pass:
Once you recorded the quartet (piano, bass, drums and guitar) outlining your song's chords, you can overdub using PARTs 9-16... For example, outline 16 choruses of fast blues changes... then go back and overdub two choruses each using the single Parts stored in PARTS 9-16.

Press [PART CONTROL] the PART SELECT button will allow you to select any PART 1-16 for realtime play. Notice you can seamlessly transition between these single Parts - you are soloing with your right hand and can use your left to switch between the PARTs without interruption or glitch...

Once you have a scratch idea down, save as .MID file and drag and drop it into Cubase for further development.