Try to demo/listen for yourself if possible. Search for 'yamaha montage m versus modx' and you can find several good videos that demo the difference. But you really need to try one for yourself to see if you like it.

But the one question you didn't answer is WHY you want a new synth if you currently have 'no problems'?

What are you looking for in a new synth? How do you use it? Live gigs? Home studio?

are there many more sounds and improved sounds over the modx.

Yes - there are many more sounds and a vastly improved audio interface. The M models also have an AN-X engine so there are new sounds that make use of that.

  is the montage m very difficult to operate. 

Depends on what 'to operate' means. Since it has more front panel knobs and controls it is actually easier to operate and get things done for performances that have already been set up.

But those extra knobs and controls mean there will be a learning curve to get up to speed just to do what you already know how to do. The navigation around the menus and screens is different. But the basic workflow is the same.

Creating your own sounds is going to be just about the same - a steep learning curve if you haven't done it before and lots of hidden 'gotchas' along the way. But the results can be rewarding.

One potentially big addition is the free ESP soft synth you get when you buy an M model. This is a software equivalent you can run on your computer that has most of the same functionality that the synth itself has. So if you use a DAW or other computer audio software that can be very useful.

Operation of the Montage M is not much different than the MODX.  There are new bells and whistles but essentially everything you do on MODX has familiar "DNA" in the Montage M.  I don't want to downplay the new "stuff" - there's a long list of wishes I've had that have made it into the Montage M but a lot of these are not things you may casually encounter.

The sounds AWM2 and FM-X (two engines your MODX has) are heavily leveraged from the past models.   There are a few new sounds.  You can probably run through what's new (in the AWM2/FMX categories) quickly.  The major source of new material will come from the AN-X engine which didn't exist in previous models.   You may relate to AN-X's presentation of synth editing more than AWM2 or FM-X.  So this may make thinks easier to edit if you relate to the new engine.  Otherwise, you can use the presets and combine those in different ways as you have been (primarily) doing.

There's a new navigation menu in Montage M that may make things easier to find.

The graphics (screen) over the knobs may help make things easier.

Then there are items that are differences in MODX and Montage (even Montage classic).  Montage will show you on the knob where the encoder is.  Montage gives you access to all knobs and sliders where MODX banks them in groups of 4.  Montage has some additional buttons on the control surface that MODX cost saved+simplified away.   This could go either way if you like the simplicity of MODX vs. power of having more controls at the ready.

Montage has a ribbon which you may find useful.  It's got new features this time around where there can be "zones" on the ribbon to act as a 3-way switch.

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