Maybe relevant to add: I purchased the a w7v and w8v file which should contain the waveform data. 

Preset waveforms aren't available as files. And w7v/w8v files only contain user waveforms so they won't contain preset waveforms either.

To use the original waveforms you need to use the Motif Rack as the sound source and Mainstage to play the sounds.

Or you can use a sampler to sample the Motif Rack waveforms, one at a time, to create your own version of those waveforms and then import your versions into Mainstage.

Please provide more detail about what the goal is. Are you wanting to use Mainstage to produce that sound without the Motif being connected at all?

The original sounds are available in a few promo packs released by Yamaha but I haven't seen anyone who's decoded these to a more raw format.  So you may be able to get the data but getting that data in a form useful to you is the challenge.

The last hardware that could play these formats was the Motif XF.  Support for these formats was removed in Montage Classic and not restored in Montage M (still removed).

So, you don't need a Motif Classic necessarily.  You can use a Motif of any generation (ES, XS, XF) or MOXF (and probably other pre-MODX "MO" keyboards) with the proper promo pack to get the PowerGrand back.  

With SampleRobot supplied with Montage - I wouldn't be surprised if someone had Powergrand tucked away for the Montage somewhere.  

Surprisingly the Powergrand isn't on the free Motif XF Performance pack Yamaha made available for Montage.

Nope.  Lots of older cherished content didn't carry forward.  Some onesy twosy individual "voices" were done by easy sounds.  They wouldn't (necessarily) have the means or license to do the presets.

I do have a Motif XF and the right expansion pack so technically I could use SampleRobot to make myself a power grand.  But I wouldn't share it due to licensing red tape.  So ...  Good luck is all I can say.  Finding a used and even broken compatible keyboard or rack unit (as long as MIDI works and can load the content) can get you a platform to sample.

It may or may not be worth the hassle.  Maybe also look for a free vsti that gets a similar piano sound. 

Thank you very much for your replies, really helpful! 

I want to combine it with the Roland RD-1000 which I already have in MainStage.
Together it should become the Elton piano sound.

Reading your feedback probably leaves me with another VST which has a PowerGrand sample included.
Anyone familiar with Gospel Music MK sensation Xtreme? It claims to have the PowerGrand, wondering how accurate it is.
Buying the rack is too much of a hassle, I already have an XK5, Nord, Kronos 88 and a 1913 upright piano shell (>100kg). 
Love all of that, but adding more gear is not an option...

Last I looked Gospel Musician took the Power grand straight from Yamaha and didn't alter anything so it wasn't compatible with Montage or MODX.  I don't know that they did anything beyond that so the power grand they offer would only be good up to Motif XF.

Maybe @Jason can make sense out of these files - Remove the hyphens to get a valid url.

-h-t-t-p-s-:-/-/-w-w-w-.-m-o-t-i-f-a-t-o-r-.-c-o-m-/index.php/forum/viewthread/473177

I got to that link via this old thread that @Jason replied to.

https://yamahasynth.com/community/modx-series-synthesizers/powergrand-modx/

There are multiple files you can download.

ClassicMotifVoices.n3.X3V.zip - top of page - this contains a performance named 'PowerGrand' and the file loads on our Montage M8X.

There is one part with 4 elements but each element uses waveform #64 'CF3 Flat Hard St'. Each element has 2 parm mods:

1. element 1 - Elem Group=1, Note Limit C-2 to B1

2. element 2 - Elem Group=2, Note Limit C2 to A#3

3. element 3 - Elem Group=3, Note Limit B3 to G5

4. element 4 - Elem Group=4, Note Limit G#5 to G8

We have no knowledge about how that PowerGrand performance/elements might differ from the original you refer to or if waveform #64 is the same, or similar, to what was used in the original.

But that X3V file does load to an M8X without error and the performances appear to be valid.

At the bottom of the page there are two files with XS Preset Voices. Neither has a  'PowerGrand' performance.

Just download and see if it works.  You could look at the free JM tools to read the sample formats and get a sense of if it will work or not.  Unnecessary if you load it up and everything works (chromatic scale through 88 keys sounds right). 

Do you know if Yamaha 'Load' operations typically perform 'on the fly' conversions? That ClassicMotif.. download is all AWM2 and the PowerGrand loaded uses waveform #64 'CF3 Flat Hard St'.

But in the Modx and classic Montage data list docs #64 is 'S6 Stretch mf L'. So if anyone downloads that file and loads the performance it would be interesting to see what waveform number is being used when it loads on a different model.

Waveform #38 for both Modx and classic Montage is that same 'CF3 Flat Hard St' which is waveform #64 in the M8x. Couldn't edit previous reply.

That Motifator thread doesn't have any samples in the "voices" so these are just settings.  It isn't what was asked for which would include the samples too.  What's going to happen is that Montage is going to plug in the "closest fit" Presets just like was mentioned in the thread that the Motif XF would have done.  This isn't going to cut it although you could just load it up and see if this variation of a piano is worthwhile for anything.

To my understanding (which is now many years old) - there isn't a powergrand sitting out there waiting to be plugged in that's been converted or resampled from the original content.  I could be wrong.

There's a video out there "MOTIF Gospel Sound Pack (MONTAGE/MODX) - Version 4 Overview" where a PowerGrand is demoed.  What this is are his own custom samples (not PowerGrand) but using the PowerGrand's programming in terms of AEGs and such.  The comment in the video is that if you try to load the original samples (due to LPC encoding) - they won't work.  This is the problem to overcome and the "best" way around this to retain as close to the original sound is to resample a Motif XF playing these sounds and develop a new set of samples.  Probably sample through a digital path instead of having additional losses through the DAC.   

There's a Nord user who I believe has done this and released a Nord version of the PowerGrand for Nord.  He has raw samples and those same raw samples could be packed up into a Yamaha (Montage) compatible Waveform/Library.   Search around and see if you find anything.  I haven't searched in a while and don't know if anything exists yet.