Oh wow, I don't feel any brightness you experienced with my zsn pro. It is brigther for sure, but its way less than zs6 level. I would even say the treble is pretty smooth and I am using the starline tip that came standard on the box. I like the zsn pro sound better than zs7 and c10 actually. Not saying them bad, but zsn pro sounds pretty complete for me. C10 has great treble and airy, but lacking in the bass. While zs7 lacks in treble extension, but has sweet bass.
At least with mine pair of ZSN Pro, and sources, i feel like the tracks have the cymbals ahead of where they better be, more sibilance than the ZSN and a brighter and harsher experience overall.
Something in the vocal is smoother ( lower 3k ), something else is not ( the 5k peak of the graph is definitely there ).
My pair of ZS6 is darker and smoother than that, but less airy and full, perhaps also because of lower 5k to 8k. They are very uncontrolled above, but react better to higher impedance output, foams and are easier to be EQed. I not using them, nor recommend to using them, as stock.
I'm not saying that the ZSN Pro are garbage, but i don't feel them to be a good all-rounder. I still prefer the ZSN tonality and overall experience, even with less soundstage and details.
So, thinking about what i'm looking from the graphs i was pointing out,
if on the market there is a model using the same DD, but with a frequency response that show that the same peaks has been fixed to sound better ( as to me the ZSN Pro sound better lowering exactly only those four peaks, something not easy to do on portable equipments ), i think that there's actually no reasons to buy them now.
