Should you want to create a voice set and upload it here follow these guidelines.
Balance (left/right): The PF voice ideally should have an 85/15 balance between the two stereo channels. The PNF (PM) is best with a 20/80 balance. That way you hear the voice coming from the most logical locations.
Volume: Check the volume of the default files, try to get as close as possible.
Format: Wav, stereo, 32 bit, 44100 Hz
Set: The voice set should contain the complete set of PF,