You have to do these first before getting WAV files to your S8300 (actually it's the G700):
1. WAV format should be in u-Law (default)
2. Enable the announcement board (V9, in the MGP)
3. Enable the FTP (filexfer) to that board)
4. Take note of the MGP IP address
After doing all of the above, just FTP the WAV file to the MGP IP address just like you would do to a VAL board.