Hmm, honestly there must have been something seriously wrong with OP's pair, or a revision down the line, because doing -6db on the highs and +3 on the lows sounds absolutely terrible, extremely muffled and boomy. I'm not a giant expert but I have a musician's ear and use SHP9500, kanas pro, toneking earbuds etc, I use Yam's MSP5 since 20+ years and while this 100$ pair obviously can't compete, it sounds like a cheap but decent version at 0/0 and HORRIBLE at -6/+3, and the proposed EQs only make it worse.
Main offender being that -9.5 at 8k, there's literally no cymbal left, sucks all the air dry.
I do agree with stuffing the ports though. Overall, it's not really studio / neutral, but it's certainly a lot better than any cheap so-called "hifi" or gaming set.