The Montage/Modx don't use any encryption/extension mechanism.

 I have read about the issue with the encryption used on the Motif series not compatible with the Montage/MODX series.

Any libraries you have that are encrypted and for use with the Motif extension facility can't be directly used on the Modx.

I have a large number of Easysounds libraries for the Motif XF. Has anyone ever made a list of which libraries are fully compatible and which are not?

Easysounds should be able to tell you which of their libraries can be ported to the Modx and which can't.

I could replace them all with MODX versions, but that would be prohibitively expensive...about $500!!!

Check with Easysounds to see if they have any discounts for upgrading.

I understand that if I purchased the MODX versions I would get some additional functionality, such as SuperKnob and Motion Sequencer mappings. 

That is also where Easysounds can tell you which of their products take advantage of Modx-specific features. The 'Pure Analog Circuit' in the Modx makes a lot of sounds better just on its own.

Just an FYI - the 512 Motif preset performances are already freely available as a download from Yamaha's web site.

 I have read about the issue with the encryption used on the Motif series not compatible with the Montage/MODX series.

     Montage/MODX isn't compatible with some of the older libraries (primarily libraries released by Yamaha themselves as promotional material) due to no longer supporting certain sample encoding types that were employed before (fair to call this "encryption" if you want -- it implies the end result of the lack of support) and also certain bit rates.  So older material might have samples no longer compatible for one reason or another.  Primarily this impacted all of the original Motif libraries (so pianos carried forward from that era don't work anymore and haven't been resampled and made available by anyone I am aware of - "power grand" for example).   And there are various packs like "Inspiration In A Flash" which has lots of content that doesn't work due to using WXC - no longer supported.

    So .. yeah, some packs don't work.  Easy Sounds will probably work with you if you have purchased content from them before and it doesn't work anymore.  Depending on what tools they had available to encode those packs - you may be good.  Lots of packs are just drop-in.  They do have newer refreshes of the packs with more features taking advantage of MODX's new buttons and knobs but the same basic content is still there and you wouldn't be losing much sticking with what you have assuming it works.

     At some point I had some kind of list going and was hoping folks would chime in what works and what doesn't.  Some of that happened and some didn't.  I'm not aware of a comprehensive list.  It'd probably be quick enough to load what you have and see what still works then knock on Easysounds (or the content provider assuming they're still around if not them) and see if there's an update available that works.   I'll go out on a limb and guess most of your content will work OK.

     You can more or less figure this out by getting the demo version of Melas tools (or use the tools if you have them from the Motif XF days) and look at the libraries in there.  The encoding type will be noted.   If it's LPC or WXC it's not going to work.  If it's 8-bit it's not going to work.   The Melas tools should be able to tell you if the samples in your content is encoded with LPC/WXC or 8-bit samples.  And if so - that sample is going to be silent.   At least that's one way to go poking around.

Thx for the answers, I was going to contact Easysounds anyway about their upgrade prices.

You are doing the right thing by gathering all the info up front. No need to invite 'buyers remorse' needlessly.

But before you spend any money upgrading your sounds you might consider buying your new synth first.

Then you can try loading your sounds and see which packs give you problems.

That should inform as to which of your packs you need to replace or update.

Even if a pack loads onto the Modx you need to consider that there may be a 'Modx-specific' version that takes advantage of the advanced engines and sounds in the Modx. Not only does the Modx have seriously updated audio components but the preset waveforms are also much better than what older instruments had.

An older pack may use what appears to be the same 'waveform' but the version of that waveform on the Modx may have more, and better, samples and could also be velocity-mapped. So an older waveform could have one sample for every 6 keys while the new waveform has one sample for every 3 keys. The old sample will have to be 'stretched' more to cover every key.

And even the 'one' sample for every keys could really be 'three' samples that map to different velocity ranges (e.g. 0-30, 31-60, 61-127). So even though both the old and new sounds appear to use one 'waveform' in reality the new version might have six available to choose from.