Ladies, gents,
I do understand your interest in changing and improving things. But when I spend good money, I want the earphone to perform right out of the box (that's why I have never heard of a Sennheiser earphone mod). Great value are the Brainwavz B100, a well reviewed, balanced and very fluid sounding single BA driver earphone.
I also prefer the Fostex TE02 as is, as it is a textbook example of a neutrally tuned and balanced earphone. I like to use it as a reference standard for comparison purposes. I also like the Tinaudio T2 as is for that reason. In my experience, any mod comes with a tradeoff: one thing is improved but another one goes missing.
I did the Slater mod for the KZ SZ3...or I attempted to...as mine did not contain any foam to be removed. The ZS3 sounds like hell to my ears: harsh and dark. I did the micropore mod on the SEAHF AWK009 and...oops...poked the needle right through the grills, unfortunately...which made no difference in the end (nothing damaged, I mean).
The KZ ZS5 and ZS6 are a joke to me (meaning, it is my personal opinion only, yours may differ). They look great ("placebo effect") but the ZS5 has tinny mids and the ZS6 has piercing treble. In the end a waste of money for me as I use the [for me] infinitely better sounding Brainwavz B100 instead.
Nevertheless, everybody has the odd earphone in the drawer that is so horrible sounding, lets say agressive, that a mod is warranted. Thanks for your good ideas here. My issue: where in Canada can you buy micropore tape, London Drugs and Shoppers Drug Mart don't carry any, and amazon.ca sells that stuff in truckloads only.