The core sample set of the Motif Classic is not inside the MODX. Some of the "best of" stuff was carried forward as far as Motif XF in the form of expansion sound packs for those keyboards (and previous keyboards). But Montage/MODX dropped compatibility with those - so things like the Motif Classic piano sounds unique to that gen are not in MODX nor is there is a supplementary pack with these that is compatible.

There are things carried forward or very similar from the Motif Classic days. There's not, however, an automated way to just import that material in.

I had the second generation - Motif ES (actually a MO6). And even this gen I had to manually convert anything I wanted over. I was able to find preset samples that were close enough and the original structure (parameter names, values, etc) were close enough that I could put humpty dumpty back together again with a lot of work. I manually mapped which screens in my MO6 mapped to which parameters in the "MODX". I could then manually construct what I needed using pictures from my MO6.

That was a lot of work so I only kept a few of the Performances that I felt had lots of original work to construct. Otherwise I started from scratch.