I see that second Alt key. But it doesn't appear to do anything different than the Alt key to the left of the space bar. In both cases if I hold down the Alt key I get a symbol like a speaker with an outline of the upper left corner of a square. If I then hold the mouse button the time indicator moves and I hear that track solo.
But there isn't anything I seem to do that moves the audio layer in either direction. I'm stumped.