The easiest way to hear your Montage is to have direct monitoring turned on and studio monitors connected to the Main L/R Outputs. Alternatively, use headphones. Direct monitoring is still needed.

I had the same problem. Try this input and stereo buttons to change.

I send screenshot

https://photos.app.goo.gl/SFjwdreLyJNMCVESA

I've connected the Montage 8 to my macbook using a midi cable. I can now record into Logic Pro X. However, I can't hear what I'm playing. There's no sound. I've tried different outputs - my laptop speakers, my MOTU audio interface with speakers connected to it. Once I've recorded, I can play back and hear what I've recorded, but I can't hear what I'm playing without having recorded it.

Help, please? Thank you!

Your question is really about using LOGIC PRO X and the MOTU audio interface.
If your MONTAGE is delivering data to your computer via a MIDI Cable, you must have configured correctly to record MIDI data to Logic. We assume, you are using something to convert the 5-pin MIDI to get it to the computer (hasn't been a computer with a MIDI jack in quite some time). Often Audio Interfaces also have 5-pin MIDI In/Outs for external gear. Is that how you are setup (?) Since you can record - we will leave that alone for now.

But audio is an entirely different animal. You should connect the audio outputs of the MONTAGE back panel (Main L/R) to a stereo input pair on your MOTU audio interface. Your Monitor Speakers should be connected to the OUTPUTS of the MOTU audio interface. (Forget about your laptop's speakers (they are not used in this scenario, at all).

In order to hear the MONTAGE you must configure your MOTU Audio Interface to allow you to hear it. As Audio Interface it is responsible for delivering external signal to the computer, converting analog signal to digital, and it is responsible for converting digital output from the computer to analog signal that your Monitor Speakers can playback.

If you are recording MIDI data to Logic, you want to make setting in the MOTU and LOGIC. Typically, when recording MIDI from an external device (like MONTAGE) you would work with LOCAL CONTROL OFF, this means you must select a MIDI Track in your DAW (Logic Pro) and route the signal so that it "echoes back" to the MONTAGE, the audio outputs of the MONTAGE will send signal to the MAIN L/R Outputs which go to your MOTU Audio Interface... and it is there that you must route the signal through to the MOTU Outputs and on to your Monitor Speaker.

Contact MOTU - ask about how to monitor a device connected to its analog inputs (Direct Monitor is the feature that will allow incoming signal to go directly to the Monitor Speaker outputs -- this lets you monitor your instrument with zero latency).