You actually double clicked? The Corrections editor should open. If it doesn't try right clicking and choosing Open in Corrections. But that doesn't work for Scorefitter, only normal music.
You can also double click on the audio drop zone to open the current selction in Corrections, but again, you can't do this with Scorefitter. You woul have to render out the music as a wav files and use it as such.
Scorefitter music should be normalised, so I'm assuming you want music that is quieter than the "correct" level?