AC3 problem: sound good but no voice (5 channels vs. 4 speakers)

[mikelats]

Hi, I got this file whose audio stream properties are: FAST Multimedia AG DVM (Dolby AC3) <0x2000>, 48000 Hz, 384,000 kbit/s, 5 Channels. That's the problem I think, as it is 5 channels and I just have 4 speakers (and the SubWoofer). So the audio is perfect except for one thing: I can't hear the voices. How can I solve this? I thought of extracting the audio and somehow changing its format so I can hear it, but I can't figure out how. Please help!!!

EDIT: I've just realized that some other files that used to play well (AC3 5 channels files, too) have now the same problem: all audio is good except for the voices. I didn't even know they had 5 channels until now...