Super or Enlightening Miracle Cubes?

What exactly do enlightening cubes do? I've heard several things like they higher then chance to get primary lines on lines 2 and 3, or they give a higher chance to get 2 of the same line as in str and str or dex and dex. I'm in a similar situation, my Tyrant Cape is legendary and i need to cube the silent crusade face accessory to legend from epic. I Don't know if i should wait until enlightening cubes to cube the cape and use my remaining supers on the face accessory trying to get the tier up or just use my supers on the cape and hope for the best.

In the end i'm just hoping for 2 useful lines on the cape and face

The bolded part.