Well, you might want to make sure that you have your little lights set up like this... these things are subtle, but they make the difference. Check out this screenshot. See the green widgets on the left side? Those control whether the track is on or off when you play back you final cut in the timeline. You can click them on and off if you just want one channel or the other, or just don't want to see the video track or whatever....
But slightly to the right is probably your problem.... See how some things are yellow? The yellow icons control which tracks are recorded onto.... and can be clicked on or off in the same way.... so, the way it is now, if you insert a clip, it will put the video track on V1, the left audio track on A1, and the right Audio track on A2. I suspect that your Audio tracks have no yellow thingies. Might want to set them up, and assign one to the left, and one to the right, eh?
Hope that helps. If it's totally irrelevant, feel free to ignore me.
EDIT: Oops. I'm sorry. I just noticed you said "Even in the viewer there's no sound"... in THAT case....
"AdamByte Helps Out," Take 2... and Action!...
When you go to the "Log and Capture" window, check out the "Clip Settings" tab... make sure that you have "Aud+Vid" selected... otherwise, your Mac is just capturing one or the other!
whew! how's that?
