Well, I am not sure why you recieved the messed up files. However, use BeSweetGUI. It is much simpler to navigate. You select the AC3 and where you want the WAVS to go. Hit the AC3 to WAV button, sit back and watch.
I figured out how to recompress the files, unfortunately now they sound like the chipmunks. So, I'm tinkering with that.