As far as I can tell I've done everything correctly. I have a rename-config.rpy, rename-config.rpyc, the voice over.rpa (and the recolor.rpa) in my games folder.
The game otherwise plays sound (music and birds chirping, etc) but no voiced lines. Considering that the mute options are in the preferences menu, I'd have said it must be working just that nothing is voiced. The options in the menu are all greyed out but I've played around with them a bit, too, just to test.
Tried it on a clean install and new game as well.
The readme states to delete a "rename.rpa" from my game folder, which I didn't have to begin with. Otherwise, it mentions to "move voice_over.rpa and rename-config.rpy to your /FriendshipwithBenefits/game". The folder where I have the game installed is named differently but just for the sake of being thorough I've named it like in the readme, even moved it into where it would be if I had it installed via Steam. No dice.
Steam guide also mentions something about an addition in the config to get around a bug on the farm. I've not done that edit for each of my attempts to get this to run, though that shouldn't matter from what I've understand.