I can affirm that the M has noticeably better sound quality than my Nord Stage 4 (which I sold immediately). All my fellow band members noticed it immediately. 

8 vs 128 elements means you can now have a single part contain more velocity layers.   Or you can chain longer sequences (cycle) of samples with subtle differences so it seems that randomly you get some "character" response.

I'm not sure which Performances exploit the possibilities.  I would start looking at high element count Parts and see how they are utilized.

Of course if you don't yet have an M series (like me) then you can't do this.  This is where it would be nice to have a breakdown from Yamaha to demonstrate an example of one of these Parts.  This would provide pre-sales potential owners to get a better idea how (more tangebly) the AWM2 improvements allow for improved results.

I can understand how the AWM2 improvements would support the marketing statements.  But not everyone would (or should) be able to visualize this without a concrete example.

Did somebody notice this ultra-high-definition sound  compared to a montage classic ?

As Stu alluded - a lot of people have noticed it - this was/is the marketing hype

[PURE ANALOG CIRCUIT 2] The upgraded Pure Analog Circuit included in MONTAGE M reduces noise and improves the dynamic range, crosstalk, low-frequency phase, and distortion rate, resulting in clearer sound at all volumes. You’ll also find the sound has more detailed low-mids and presence.

There is definitely a big improvement to my years even for sounds that haven't changed in the new model. Sounds are much cleaner and crisper to me.

A major improvement is the ability to use the sliders for ALL 128 elements in groups of 8. Another major, for me, is you can now mute and solo all 128 elements. Before that was only possible for the first 8.

I'm not sure which Performances exploit the possibilities.

The original Blake's take has links to several videos that do that in addition to the usual/expected marketing angle

https://yamahasynth.com/learn/montage-m/blakes-take-introducing-montage-m/

I would start looking at high element count Parts and see how they are utilized.

The Chordz 2 Chill 2 has the highest count at 67. It maps several sets of 8 elements to different velocities with each set using different combinations of detune to produce different sounds for the same key.

Most every key plays what sounds like a 5 or 6 note arpeggio if you press the keys slowly.

When you audition it watch the scene buttons, the part mute buttons and the rotary encoders under the sub display and you can see them all dance around. Not sure how practical the sound is but it definitely demos the sorts of things that can be done.

(not that it matters necessarily...)

BTW: I wouldn't consider PAC as a part of AWM2.   Sure it contributes to a higher fidelity in the sound but is not, in my opinion, any part of AWM2.   It's debatable of course but an output stage shared by all 3 engines would seem to be something outside of AWM2.

Montage classic is fairly close in terms of AWM2 in the Motif XF that came before it yet the same exact "patches" from Motif XF are said to sound better in Montage classic without any change in AWM2.  This is all about the analog output.

BTW every generation is a stepping stone to the next thing.   I know the direction of AWM2 is leading towards an AWM3 that can break some of the core limitations.  I'm not sure how far M will go in terms of future updates but am certainly looking forward to where this leads over the coming years.

Yamaha say they improve definition of the AWM, this make me curious, how? , did they provide technical information about that, I mean numbers. I don’t have a new M, only the first version and no shop in my island to try one, and thru internet, I don’t think you ear can realize this improvement. Just curious, and looking hopefully for some upgrade in some futures line.

I find nothing on the net about technical characteristics of this AWM ultra hight definition, just I can guess there are more  data bits than it was in the first montage ?

More elements per Part.  That's the technical detail.  Was 8 now is 128.

This is largely underutilized at the moment so there is bound to be content that takes more advantage of this capability.

The other AWM2 improvement is that user loaded content gets its own polyphony pool.  Therefore combining user and preset AWM2 doubles your polyphony.   128 to 256 (conditionally).  That's the technical detail.

Even ignoring a new engine (AN-X) there are many improvements over the past Montage that fall into what I would consider to be tangential to AWM2 and not AWM2 itself.   More destinations in motion control, etc.  

But nothing about ultra high definition…..

That could refer to the increased resolution of the controllers from the range 0-127 to the range 0-1023 to accomodate the migration to MIDI 2.0.

The OS 2.0 update added that resolution change, a new MIDI 2.0 port and support for the UMP data format that MIDI 2.0 uses.

Oddly I noticed that the resolution for user curve values also increased to 0-1023 but since you still only have 8 possible steps/values I don't see that as being very useful.

Yeah, I've commented on the need to increase the resolution for the new M as well as the previous gen when there was still a chance to make changes.   Hopefully user curves get a way for more free edits. (full res editing or maybe just different shapes which would be a huge compromise but still better)

BTW: I've been suggesting that more elements per Part gives you higher resolution which is analogous to higher definition.   Marketing teams are coming up with terms and they aren't always literal.