@Fahim Foysal
I feel like that bit above comes of moderately harsh. I'm obviously pretty interested in the mechanics of hearing myself, and I'm certainly not trying to dissuade you from exploring the subject but I feel like you're overthinking your experience a bit and you should take a bit more notice of what you hear, instead of what you think you should hear
An enormous amount of information has been shared in this thread and it can be pretty daunting but like, you shared your experiences only very briefly with the ZS5 so it's really pretty hard to figure out what else you might be looking for.
You've got some ZS6s on the way right? If you're dissatisfied with the ZS5s, why not take them to task with some simple changes?
You mentioned you feel they're particularly lacking in bass, so how does taping the vents treat your experience?
You mentioned some over expression of some frequencies - there's plenty of graphs floating around to give you a general idea of where peaks might lie. What has your experience been like toying with some EQ to bring them in line?
Have you tried some cheap foam tips? How do those treat your experience with the highs?
Tip rolling in general?
Source matching? What's your experiences with sources been like?
Cables? I still feel like this should go at the bottom of the list but?
And then with a better handle on where you might want to make changes, if you feel like it, you can get more drastic or semi-permanent with, for example, things that Viber and Slater have gone into in depth relating to various damping setups.
Maybe you'll find a setup you like, maybe you'll just come away with more information to understand better what you want to hear, either way you come out ahead.
And not really related to this thread so much but I believe you mentioned the Xiaomi Pro HD... tape? tips? Why didn't you like them compared to the ZS5 or w/e else you can compare them to, etc.