Select both clips and your audio in the event browser. Make a multicam clip with all three selected. Verify in the angle editor. Also what helps is to label the clips according to their angle. You can now edit the clip into a project. open the use Shift CMD 7 to get the multi angle view up. Select the audio clip first. Then in the upper left corner of the multi viewer change the switch setting to video only. Select your first angle. Begin playing and cutting between the two video angles while playing. In the project you will notice that they are two sets of dotted lines at each cut, white and black.The lines will show you where edits are made in relation to time and whether edit affected the audio or the video.
I used this process recently to cut a 1 hour live show performance with the audio taken from a mixer. took about 90 minutes to cut.
