That's true, but you can still add a new mono track to be the new Audio 1 and move the music clip there. Just right click in the first column of any audio track, or use the Sequence drop-down menu.
You don't even need to move it up to the first track to adjust the gain keyframes on the rubber bands (paths the keyframes form). Just click the little arrow on the left of the 'Audio 4' label on the left to expand the waveform. It'll look just like Audio 1 except monaural.