The CP88 and Montage have essentially the same tone engine properties. Both are the same core AWM2. The primary difference is going to be the sample set used. The CP88 [is reported to have] a different sample set. It does sound slightly more "detailed". I'm just basing this off of an A-B test between MODX8 and CP88 - which isn't quite fair because MODX's output stage isn't, I believe, as "buttery" as Montage's which would have been a better candidate. And feel is out of this A-B because I was listening to a recording and focusing on the core sound - not transitions between velocity layers or those sorts of things. I think the new CP series did a sampling and/or post-processing "redo" of the work that made it into Montage and MODX. It's nasty to mid-stream transplant from one series to another because you could negatively affect users who like/prefer or have built their sound around the existing Montage CFX. If we're going to see an expansion with the CP series content for Montage is anyone's guess. Probably not anytime soon (cannibalism).

The other big difference for piano between the two is the keybed. To me the biggest factor is CP88's triple sensor with no aftertouch vs. Montage's double sensor with aftertouch. Aftertouch is not a CFX thing - so that the CP88 is missing aftertouch is of no consequence in this comparison. But triple sensor can make a noticeable difference in the restrike behavior as more "piano-like" in the CP88 vs Montage. Having recently tried the CP88 - I can say it's one of my new favorite keybeds. Better than Montage's which was my previous favorite. Something seems even more responsive about the CP88 - outside of the sensor. With the keyboard off and playing with no sound - I like the feel of the CP88 better. I do this to keep the keyboard from giving me false impressions based on velocity curves, sensors, etc. as one test before or after playing with all of those other features "turned on". This is subjective however - you'll have to see for yourself.

Neither keyboard have sympathetic string resonance. Since both use the "same" underlying tech for sampled sounds - they both share damper resonance. From a "resonance" standpoint - even though either one may have slightly different tweaks to the effects - they're basically on the same level with respect to resonance features.

The CP88 and Montage have essentially the same tone engine properties. Both are the same core AWM2. The primary difference is going to be the sample set used.
Neither keyboard have sympathetic string resonance. Since both use the "same" underlying tech for sampled sounds - they both share damper resonance. From a "resonance" standpoint - even though either one may have slightly different tweaks to the effects - they're basically on the same level with respect to resonance features.

Are they using the same resonance effect? Is there anything documented to suggest they used the same exact resonance effect?
Having the same features for resonance, but having not the same effect used, they could 'sound' completely different, even if the features are set the exact same way...

Basically, after watching this YT vid https://www.youtube.com/watch?v=mpsPQ6OjcqQ of a professional classical pianist that normally reviews acoustic pianos, but did a review of the CP88 & said he loved the resonance on the CP88, which means it must 'sound' fairly authentic to an actual CFX grand.
Just wondering if the Montage's resonance effect is & 'sounds' the same as the CP88..!?

The Epic Grand piano's PART based resonance sounds fairly realistic and a bit different from the Montage resonance effect. I am wondering if I would get closer to an authentic resonance sound using a combination of the Montage's resonance effect + the Epic Grand's resonance PARTs!? However if the Montage is already using the exact same resonance effect and 'sounds' the same as the CP88, then by extention, the YT acoustic grand expert has basically said that Montage's resonance effect sounds most authentic to an actual grand, and there would be no need to combine the two types of resonance effects I mentioned above in order to get it to sound even more authentic...

How something sounds is subjective - but both use the same technology. If you turn one instrument all the way up and the other at mid level - you create a difference in "resonance". Reverb settings - same thing. EQ would have an impact on perceived resonance. The room. Anything. So saying there could be some minute change which drastically changes the character of either instrument is valid on just about any dimension. I'm only covering that both are built on the "same" chassis. The most remarkable difference being the sample set used. They do not use different technologies.