> But if you can't tell the difference already, what "breakthrough" could possibly improve the experience?
Well there a lot of things you might want to do spacially, or spectrally, with the sound to spread it across different speakers, etc.
The problem is, once you encode audio with a perceptual codec like MP3, the resulting audio makes sense to the human ear in a very specific set of circumstances: that it's played in stereo through a standard listening system.
Outside of this, it breaks down.
The reason is straightforward: MP3 primarily removes parts of Sound A because Sound B has played before, or simultaneously, making some parts of Sound A inaudible ("masked").
Now, if you go changing the sound, dividing it between speakers, extracting elements, etc, the Sound B is played back differently and hits the ear differently, meaning different parts of Sound A get masked, and the parts the MP3 cut out of Sound A become obvious (it sounds akin to an MP3 with a 64kbps bitrate, or crap YouTube vid, with all the swirling noise and distortion).
Similarly, if you need to digitally analyse the sound for some reason, the loss of data is very significant, as it was encoded to sound good for a person, but the signal doesn't make sense in its own right - the removal of all those chunks of audio looks like weird noise added to the signal.