(From the project window)
There might be a few people who don’t know about this, I learned it not too long ago and use it a lot:
** Select both tracks simultaneously
** Click “S” on one of the tracks.
** While project is playing, keep one finger on the “windows” keyboard key, and hit the “S” keyboard key repeatedly to A/B the two tracks.
Not sure if there is a Mac equivalent? …
Hope this helps someone - I love it!