So, my ER4 came back from the shop and I'll be going back to it as my daily so I probably won't be using my ZS5 anymore. To those curious about what's inside and to put the questions to rest, I decided to open them up to see what the fuss is all about.
This is the V1, so the wirings maybe different compared to the V2.
Before opening them, I went ahead and remove the metal mesh filter. Based on what I heard, the entire soundstage and overall signature is shaped by the filter. Removing it would be detrimental to the overall sound.
Next, I went on to prying it open and started cutting the wires one by one to see what I'm getting out of the drivers.
From what I heard:
The Inner BA Driver either does nothing, or as KZ claims, reproduces ultra high frequencies that I certainly can't hear.
The small dynamic driver does actually contribute to the sound, but an incredibly small amount considering what it is technically capable of. It only handles the part between 1khz to 3khz, about where the mids starts peaking. The effect is hard to notice unless your're aqquainted with the original sound.
The BA at the nozzle does indeed work as intended, and it only handles the higher frequencies, especially the mountainous peaks at 7khz and 10khz. This is where all that treble energy comes from.
Finally, the large dynamic, being a full range, handles most of the work. The entire response is handled by this driver, and funny enough, after removing everything from the nozzle and listening to the dynamic itself, they produce a pretty enjoyable sound.