Audio is stored as a Yamaha-specific variant of AIFF. (That's what the 'FORM' ID at the beginning of the file means.)
The Yamaha form type is 'YTWV'. If the audio data is standard AIFF (16-bit, 44100, etc.), then the YTWV can be patched to 'AIFF' and the file can be read by Audacity, etc.
However, not all audio is standard AIFF. The Woodflute in the "Best of Europe Pack" is wave type 'WXC'. It shows up as noise when read as raw audio data.
So, it's a mixed bag.