Hi
The simplest, and most intuative way, although a bit phaffy is to first assemble your video clips and then instead of muting the whole of Audio track 1 by clicking the microphone icon at the left end, you can click the microphone icon that is on the audio track for each clip, and ticking the box marked "mute"that appears for each.
Do this for the clips you want to individually mute. Now you can continue as mentioned in my post by dragging your music clip down onto Audio track 2 and position it under the muted clips.
A quicker alternative is to assemble all your video files on Video track 1 as before. Now press down the SHIFT key and click the first clip you want to mute and then with the shift key still pressed, click the last clip you want to mute. This action will select all the clips together..(they will turn a grey/blue colour to show that you have selected them.)
Keep the SHIFT key down and right click the block of selected clips and select "Group selected clips" from the menu. Your clips are now in effect linked.
Now grab the selected video clips and drag them UP onto the overlay Video track (Video Track 2) They will all now be on Video Track 2 and their audio will be on Audio Track 2.at the bottom.
Mute all of Audio Track 2 by clicking the microphone icon at the left end of the audio track.
When you play the sequence the overlay video (Video Track 2) will now play silently whilst the clips on video Track 1 will play their audio.
Now you can add your music.
Open the media list window audio files and drag and drop your music clip onto Audio track 3 which is underneath the muted Audio track 2
Drag it right or left to position it under your muted clips....and that's it.
It takes longer to describe than it does to actually do. If you don't have many clips to mute, then the first method may be just as quick.
Nat