I have another question, I want to control the Montage with a second MIDI/USB keyboard. Does it have to be MIDI or can I connect a device with the both USB-connections instead? Because for example, the M-Audio Oxygen 49 MK4 doesn't have a MIDI-output.

What 49 MIDI-keyboard would you recommend that can control multiple zones of the Montage?

@Robin

... in this other thread, you had asked for 49-61 key keyboards - so I offered a few choices: https://www.yamahasynth.com/forum/master-controller#reply-19359

In 49 keys - maybe all 16 channels (zones) is not as important.

Native Instruments Komplete Kontrol S49 - m.thomann.de claims this keyboard to have 16 zones. I haven't found a spec to verify the number of zones. Two things I personally do not like about the instrument are lack of sliders and also the touch pitch/mod wheels vs. physical joystick or wheel.

Akai Advance 49 - supports 8 zones. No sliders here either - but physical pitch/mod

Yeah I answered you there also. I would like to know if it's possible to connect the external MIDI-keyboard through USB or do I have to find a keyboard with a physical MIDI-connection instead and connect it through MIDI?

I will use the Montage to control the PARTS like volume and so on, so I don't need alot of faders, knobs and stuff like that, I just need the extra keys to extend and control/play the PARTS/PERFORMANCES on the Montage.

Montage is unlikely to work with a USB-connected keyboard although I have no information to verify this. All keyboards (controllers) I suggested have MIDI 5-pin DIN connectors.

You may be able to use something like this http://www.kentonuk.com/products/items/utilities/usb-host.shtml for USB-only devices although why select a controller with only USB connectivity if others will work which have MIDI DIN connectors?