IMPORTANT FOLLOWUP:

I just received a telephone call from Manuel Dorantes to answer my above questions.
Unbeknownst to me previously, as I've been unable to find this topic covered in the Tyros 4 Manual,
I've now learned (from Manuel ) that no prior PC conversion (from Wav to UVN) is necessary,
and that you can directly IMPORT a 'WAV' file into the Tyros 4 expansion 'flash' memory,
with the Wav to UVN conversion performed automatically within Tyros 4 itself while importing.

Here's how:

On The Tyros 4 Keyboard: Voice Creator Button > Expansion Module (E button) > Import Wav (H button)

When the Wav file is imported, it's automatically converted to UVN by the Tyros 4 keyboard itself, and then stored in expansion module flash memory.
Many thanks Manuel for that informative call.
I'm really looking forward to exploring this cool feature now.