Is there a way to select multiple audio tracks and make all of them stereo pair at the same time?

If I remember correctly it is not possible modify a group of selected clips on the timeline with the Stereo Pair command - unless all the selected clips have exactly the same properties - such as being linked to video clips, etc. So you have to manually go through and select the dual mono tracks you want to pair individually or in smaller groups to be able to apply the Stereo Pair command.

If you select a bunch (a couple) of clips, and go to the menu Modify, you will see if Stereo Pair is grayed out or not. If it is grayed out, then you can't apply it to those clips as a group, but you probably will be able to apply it if you make smaller selections of clips.

MtD

my memory is that the options is not greyed out, but that it just doesn't work for multiple clips in the timeline.