I've been doing this with Avid Studio recently - but with three cameras.
There isn't a multicam mode in AvSo, but the multitrack layout and smart mode features make it quite easy.
I put the main camera with the best sound on track 4 and expand the height a litttle. I then detach the audio and lock the audio track only
I put the second camera on track 3. By studying the audio wave forms and playing the timeline, it's quite easy to sync up the tracks. Zoom right in for more accuarcy. For the final few frames of accuracy you can switch to trim mode, putting a yellow trim point at the start of the clip on track 3 and pressing the single frame buttons to slide the track left or right a frame at a time. Use the loop play clip to judge if the sync is as good as it can get.
Don't lock track 3. Mute the audio or deselect audio as an active stream. Now if you split the clip on track 3 and delete the parts you don't want to see, you can adjust the in and out points using Quick trim - green trim points using click and drag straight away. Track three will maintain its sync. Swich off magnetic snapping for more accuracy chooosing in and out points. If you want to check exactly what is underneath, click the eye icon to the left of the track to hide the video. Note that if you use split without selecting any clips, all the tracks get split and you can't repair them, but apart from it making the timeline untidy, it doesn't cause any harm.
If you've patched to AvSo 1.1, watch out for the 1 frame inaccuracy with snapping the out points.... 
Repeat for the 3rd camera on track two. This leaves track 1 free for titles. I added a track 5 and 6 for sound effects, audio repairs and music. Sometimes the audio from the other cameras was useful to patch up the main audio (when the mic got knocked, for example) so I dragged it to track 5 so I didn't forget it was in use.
If I decide I need to trim the main track, I use one of two strategies.I need to unlock the main audio, obviously. I either make sure I add a trim point to all the tracks and use advanced trim, or I use CTRL SHIFT click on the incoming clip and drag all the tracks right to make space. Work on the outgoing clip, then select all the tracks and close up the gap. This can be quicker and less confusing than using advanced trim.
Now, I'm not saying this is the best way - I'm still learning how to use AvSo efficiently. I'd be interested if anyone has any improvements on this.
You can do much the same in PS using the overlay track, but remember the track layout is reversed, with the lower tracks showing up "above" the upper tracks..