https://www.yamahasynth.com/forum/master-controller#reply-19359

I mean a master that can control montage 6 in multi midi mode and not only in single midi mode, so I mean a master that can send 8 midi channel at least at the same time and work prprely with montage6.

Get a Controller that can send on 8 MIDI Channels if that is what you want, but to clarify, you do not need one to properly control a Montage via MIDI IN. It is apparent that you maybe under the misconception that you cannot control the Montage "properly" on a single MIDI channel.

You definitely can. You can do anything when with the Montage in MIDI I/O Mode = Single as you can do with the Montage controlling itself in Multi... as concerns the MIDI INPUT.

The difference is more on the O (or OUT) side of the MIDI I/O, not the I (or IN) side. Here's what that means: when the Montage is in "MIDI I/O Mode = Single", the Montage only transmits OUT on a single MIDI channel... This means that the ARPEGGIO data (there are 8 possible simultaneous Arps) is NOT output. Only the Notes you actually press are routed to the MIDI OUTPUT.

When Montage is in "MIDI I/O Mode = Multi", the Montage transmits each of the 8 possible PART's data on separate MIDI channels, so the PARTS assigned an ARPEGGIO will Output the Arp phrase, those with no Arp will output the Notes you actually press. And the data is streamed separately

But to be clear this is on the MIDI OUT side of the equation.
On the MIDI IN side, which you are concerned with when controlling Montage from an external keyboard, there is no difference in how Montage behaves, when you control it on a Single Channel from how it behaves in Multi Mode.

You can get whatever controller you desire, but buy it for the right reason, not because you think you cannot "work properly" in "MIDI I/O Mode = Single".... Just FYI.

The reason is that I only need 88 weighted keyboard light and play it but I want to controol other keyboard by montage 6 (recalling programs etc) by midi Montage out and I can do right only using montage 6 in a multi mode midi way (because use it toghether with montage 6 internal engine)

This MIDI in equivalency for multi vs. single -- does this include controllers? I understand that notes are mapped by velocity (of a white or black key) and which of the white or black keys is struck. So it doesn't really matter if a note range and velocity range "lives" on one part or another part. You can safely "merge" all the parts together and still end up with the same result since note ranges and velocities for any given single key do not change. Ignoring that an external keyboard could play say "C3" quietly for one part, "C3" medium volume using a the same external keyboard on a different part using a second zone, while you mash down "loudly" on "C3" at the same time for a 3rd part (requiring multiple zones to accomplish). But just compared to what you can do with just the local keyboard -- there's no difference so I'm with you there.

However, what about controls? If you merge all PARTs together - do controls (PART-level assignable knobs for example) still respond to multiple incoming MIDI channels the same as non-merged (multi)? Just trying to understand because "the same" needs to encompass all aspects of the keyboard and making sure I'm not missing something.