Well as long as I can see I can not adjust video track/voice/music tracks separately:-(
Do you mean adjusting by using drop down select under 'Duration'?
You most certainly can adjust all four tracks independantly in UVS8, if you go to my website and look at the picture at the very bottom of the "Screen Views 2" page you will see the screen you need to do this.
To access this function click on the loudspeaker symbol (audio view) at the bottom of the left end of the timeline - you can then either use the volume slider up the left side of the preview screen or manually insert and move nodes in the actual audio timeline.
Use of the 'Audio mixing panel' and the 'Audio View' are explained in the help files accessed by clicking on the question mark near the top right corner of your screen.
EDIT - or better still Mike has put some pictures up while I was typing my reply.
I have the avi file (divX 5.2.1) with a sound and I want to remove this sound and replace it with mp3 sound file.
It's a pity I can't have you with me right at the moment when I edit the file, but here is what I'm doing exactly:
1. I put the file to edit line
2. Go to sound edit
3. Turn off video track (tried to turn off all tracks except music track)
4. Drag and drop mp3 sound file to music track
5. Go to 'Share'
6. Save as 'custom format' -> avi -> select divX codec -> save
7. And....when I play the file I have the original sound (people voices) and the mp3 sound file I've just added