My 2 cents...

It probably won't help you, but the one SynthCloud product I bought was a little disorganised to say the least. It came with a pigeon english .txt file on how to "assemble" the Performances.... .wav samples, Arps, Component Parts/Performances etc. In one case the composite "Parts" of a full Performance were separate, and you had to "Performance Merge" them together. Also, a lot of the Performances had identical or very similar names, but were in fact different... very confusing to a beginner. I get the sense that SynthCloud are just collected snippets of Public Domain User Patches, that they will send you, but you have to compile them yourself (like IKEA flat packs).

By contrast, KAPro and Easy Sounds were just ready to go.

As you suggested, I would try creating a User File of the performance on MOXF and then transferring just that directly to the MODX. I assume file compatability, but not certain.

Sorry, I’m not familiar with the library you have purchased and whether or not it will work for the MODX.
If you are looking for some help we need you to provide some concrete information.

What is the file extension? .X6A? .X6V? .X6E? .X6W?
This will tell us something about the data that they provided you
How many Voices are provided for the MOXF? Most for purchase libraries do not provide all 384 Normal Voices many (in fact, most) of the data are usually repeats of the factory…
Does the library include custom waveforms? If so, this affects your load options.
When you loaded the data, which option did you select?

BM said "(in fact, most) of the data are usually repeats of the factory…"

I found this to be the case with my $70 SynthCloud purchase. On close inspection, they were largely Factory Presets with only the Name changed. For example Song X Bass, another would be called Song X Lead. Then you realise SongX Lead is 100% the Factory Preset "Monster Lead", identical, even down to the redundant/orphaned control assigns and elements.

Then to get Song X you had to merge SongXBass and SongXLead together, create all your own relevant layers and keyboard splits etc etc etc. They won't be getting any more cash from me.

Thanks for your help guys. Here is their reply.......The MOXF files work only as single voices on Modx, but you can't load the Performances.

We are sorry but this is the reason why you can't find all the sounds

LOL

I could be wrong about this, but think there's some kind of way to convert MOXF to MODX/Montage such that all comes across.

Like Antony, I've used KAPro, but also, there's a Twisted Tools set that is truly phenomenal, which originates from MOXF. It works like a gem on MODX/Montage, and taught me more than I can remember.

I can't remember where I got it from, long time ago, but think it was here: https://europe.yamaha.com/en/news_events/2013/twisted_tools_selection.html

Due to this set claiming compatibility with MOX which has no user sample memory I would tend to lean towards either no samples or a superficial amount of samples. Proper labeling would have been to claim a set works for "MOX" only if there were no new samples included.

The documentation for Synthcloud packs does not very clearly give these kind of statistics.

There's another set from the same place that also claims "MOX" compatibility but shows one Performance with samples on two keys with a note "(requires DIMM memory) ". There are not similar notes on the "classic keys" set.

Proper specifications for add-on content is a general problem across the board not necessarily isolated to this 3rd party provider.