On Windows, if someone wants to, they can poke around the installed packs in:
C:\Users\XXX\AppData\Local\Yamaha\Expansion Manager\Packs\
where "XXX" is your user name. One needs to be aware, however, that YEM uses a database manager that names directories and files with Global Unique Identifiers (GUID) instead of human readable names. You can find waveform files within the pack directories. The pack directories contain two hidden files -- .index and .catalog -- which assist navigation a little bit.
If you're lucky, a waveform file may be in a standard format (e.g., WAV). Yamaha protected content is usually in their proprietary format which is virtually unsupported by third party tools. Yamaha compression is their secret sauce.
You can also find UVF voice definition files down there, too.
If you go exploring, good luck! Be prepared to deal with highly cryptic naming and be ready to identify file formats, etc. by magic numbers. Also, whatever you do,
don't change anything unless you really, really know what you're doing...
Always have fun -- pj