Easiest way to alter the sound is to use the three vent holes. More holes you close, more it tames the bass.
I placed thin piece of foam over the driver and a thicker ring of foam around it.
That brings the mids more forward and tames the highs. Because the outer foam ring covers the baffle air vent holes I removed the papers so atleast some of the air can pass through. I covered back of the baffle with blue tack to make the baffle more rigid and less resonant. I plan on replacing the bluetack with some self adhesive acoustic tape... I'd like the insides of the headphones to be as identical as possible in both cups. I removed the piece of paper tha covers the back went. That made the sound more spacious but also added too much reverbs. As a back wave guidance system of sorts I'm using ear tip from my tennmak clarinet iems.
Those iem tips are not a perfect solution and I feel that the cups still need some sort of dampening. I have not decided what material I will use. All of those mods are reversible if you don't throw away those hole cover papers. Try and fail method
I doubt any of those mods are mandatory so the headphones can be tweaked to ones liking without aiming to one specific goal.
Only thing that is a must have is unfortunately the one thing that costs money. The pads are not ideal. Those are thick(as thick or maybe 1-2mm thicker than hm5 pleathers) , soft and comfortable if you don't have big ears. If you don't have fit problems the pads are still the main reason for the excessive bass. I use hm5 pleather pads. Those fit fine but are just a bit too small.
I also tried hm5 velours but highs are a bit too much with those. Mids become recessed and mid bass looses it punch. Strangely there is still enoug subbass. With velour pads those foams over the driver are essential. Even though I decided to ditch the velour pads it was a nice experiment. Those pads show a lot of the drivers potential. Detail retrival is on par with my Sony Sa-5000 and Beyer T5p. Highs have kind of electrostat like effortlessnes...it's a shame that those are not in balance with other frequencies.
I'm not dead set on on using the hm5 pleathers. Hybrid pads might be better. If those maintain some of the air and detail of velours without leakin out the midbass and mids... I have not yet decided if I will get hm5 hybrids or hifiman focus pads.
I use the shorter cable. It is fine but very thin so I guess there might be room for improvement.
It is amazing how many obvious things there are wrong with these headphones and yet these sound as good as they do even with these unfinished mods
EDIT:
This thread might be more appropriate for future msur discussion