Hello I have been beating my head against this for a couple days now and just found the solution to my problem which I have been googling like crazy.
Turns out my output was set to 5.1 and my speakers are supposed to convert to 2.1 but due a failure in my speakers the center channel is no longer being converted. Plugged in my other 2.1 set and viola voices are back.
Just throwing it out there for anyone else that may be having problems like mine.