Using those filters would be a lot like using the thin foam from earbud covers that @Slater suggested. So it isn't too much of a surprise that you got similar results. Its nice to see that there are simple cheap mods to try. I just picked up the HiFiMan RE-600 which come with similar (identical?) filters. Although I like the sound of my ZS5 V2 and ZS6 as they are now in stock condition, perhaps I'll give them a try using these filters just to see. I would have tried the earbud foam if I had earbud covers but didn't.