Just wanted to tell you my experience, so I got to Garuda fight, but it was strange I was over level 40 and have never heard voices in cutscenes. I tried to find a solution, but my client seem to be ok, also i had every other sound in the game.

So I started to research a little and found that you have to configure your speakers so that 5.1 Surround Sound can play. I went to speakers and select configure for my active speakers (I just have a left anr right speaker, no subwoofer or any other thing)
So in audio channels I selected 5.1 surrond and click next, then on the next screen select just left and right speakers, so that all the sound of the 5.1 go through my left and right speakers.

I tryed viewing the opening movie and all set I'm now able to hear the voice acting during cutscenes, hope this work for anyone having the same problem

I live a link for you to see how you can configure speakers

Note: on the video link the configuration is done for Quadraphonic sound, but I got this solved selecting 5.1 surround

http://www.youtube.com/watch?v=Pq2oj1CcD4U