When you listen to a finished song you hear the result, not the decisions. Everything arrives at once and there's no way to tell what each element contributes, because you've never heard the same song without it. That's why plenty of people enjoy an excellent mix without being able to say one concrete thing about it.
Stem Stacker solves that with an Arkanoid mechanic: every block you break activates a stem and the song assembles in front of you. Drums alone first, then the bass comes in and suddenly there's weight, then the vocal and the mix finds its focus. That moment when one element enters and changes everything else is precisely what you need to learn to perceive.
The game part isn't ornament. Analytical listening is tiring: it demands sustained attention on something with no immediate reward, which is why almost nobody does the listening exercises books recommend. With a game mechanic, the game sustains the attention and the learning happens underneath — which is how most perceptual skills are acquired.
If you then want to make the decisions on those same stems instead of just switching them on, that's Mix Space. And to know what each layer does as it joins the rest, the spectrum guide covers where each instrument lives and who it fights with.