I found that I had to first open the file that I wanted to reduce the volume on, do the AMPLIFY - and then save under a new name. Then closed the file and used the MIX Tool to combine the two.
Now I'm finding that file lengths were different and since the low level mix file was just a binaural beat I selected the portion of the longer file that was not mixed and did mix again. Worked fine - except I had reduced the volume too much and had to redo, none the less it can be done.