Koz - The waveform you display looks like something that would pass when I first began using Audacity. Maybe a boost of 1 or 2dB would be good?
Steve - If it involves Fourier transforms, it must be analytical geometry. Anyway, Audacity is using a cube to represent a sphere? A better question is - What elements of the sound are being represented by the cube? Amplitude, pitch and duration? I mean, each line or figure must represent some element of sound. So, what are they?
In this context, “cubic” just means that it is using an equation to represent the waveform where the equation is in the form:
f(x) = ax^3 + bx^2 + cx + d
“x^3” means a value “x” multiplied by itself twice, for example if x=2, then x^3 = 2 * 2 * 2 = 8
For a more detailed description of cubic functions, see: Cubic function - Wikipedia
The only thing that ClipFix deals with is the amplitude of the waveform over time - in other words, what the blue waveform looks like when you zoom in.
Koz - I think that if that track is at -6dB, then I estimate you could mix three of those together to make one mix that just touches the ceiling. So I should be planning these projects before recording. I should plan on how many tracks will be needed and then divide the levels among those three tracks. 
Steve - What does that cubic equation represent in the physical world?
Nothing. It’s mathematics - purely abstract.