Finally got into making conversation dialogs and ran into some issues when wanting to add Voiceover with custom .wav file.
Is there any specific .wav file setting that the sound file needs to have in order to work?
I downloaded several free .wav samples from the internet just to make sure if my custom sound files aren’t broken but neither of them worked.
Stay while and listen! 
I try custom sound twise and don’t use any specific settings. All work correctly. I used Nero Wave editor with default options: 44.1kHz 16 bit stereo.
May be problem somewhere else except *.Wav
Also you can check this: http://www.grimdawn.com/forums/showthread.php?t=54180
Tried to use different .wav bit rates: 705kbps which is standard setting for GD sound files (44.1kHz / 16bit mono), and also 1411kbps (which is your Grava VO .wav files) without any success fo far.
Can you test this sample and see if you can make it work? https://drive.google.com/open?id=0B3WjRe4tUKDKYWpmR1BEWkpJUDA
Thanks.
Just try it. When i set your voice over it play very fast, then i resave it with 44.1kHz stereo and all became normal.
Also sound may be required volume up for later use.
Update: