So has anyone actually upgraded the Sparks "sound system"?

I have two 2015 Spark EV's and I'm OK with the performance of the sound system. One way that I did improve it from factory settings was to move the center of the speaker focal point about 1/2 the distance back from dead on center. It sounds much better. I know that doesn't fix the tonal qualities and speaker output that might bother decerning audiophiles but it worked for me.

I put a small sub under the passenger seat and turned the bass way down on the main car mixer. This way the high frequencies get sent to the car speakers and the low ones get sent to the sub. It was actually a really nice improvement, not too much bass but much more balanced sound.