Regarding the mids and the bass, you did not burn them at leat 100 hours, and pads MUST tight up to the ears to obtain good bass, increase the camping level, and then it will be another story...

You should also change the stock cable

"I should note this before we get started - sorry for delay in review but I need to go through this first...
Ok... after letting the Gjallarhorn and Magni break in playing non-stop for a 75hrs+ - I still was unsatisfied with sound. I decided to try something that would transform these headphones into the unbelievable high performers they could be- out of box they both were extremely comfortable (my head is large (62mm)) so I figured they were as they should be... BUT! They were not tight enough I thought- if I press the headphones inward slowly and gently- so not to deform the voice coil or membrane structure - the bass and dynamics would increase tremendously- so I decided to bend the metal band by the left and right indicators on either side evenly (see pic)."

Nope, I followed the adjustment instructions for the headband.

I of course understand that every head is different, every ear is different -- achieving proper positioning and clamp is absolutely necessary, and is a personal preference thing. I spent a good portion of my now almost entire day of futzing with these headphones trying to get something resembling good performance out of them via headband bending, manually changing positioning around my heads, changing the pressure against my head with my hands -- no dice.

Perhaps I received a faulty model. Perhaps they were damaged in shipping. However as-received, these absolutely did not rise to the price of $1350 plus shipping -- they couldn't even compete with my unmodified $450 E-Mu Teaks which have been my daily driver for several months now. I'm a firm believer that if you're going to spend such an amount on headphones, they should be at least "good" out of the box -- and /stellar/ after adjustment.

Now don't get me wrong -- I'm glad that you love your pair so much, and were able to get them to perform quite spectacularly for your needs and preferences. It was your review and excitement which led me to purchase these to begin with! Unfortunately for myself and at the time of this comment, three other listeners who have popped by to try them, they just aren't good headphones.

Perhaps their design caters to a particular niche of either listener preference or head shape.

BTW to be clear, the model I purchased was the JM edition modeled after your mods.

As for burn-in, burn-in has been shown in numerous studies to change the acoustic properties of dynamic drivers by less than 1%. Blind studies have shown zero difference between burned-in drivers and fresh drivers, and there is strong evidence that the true nature of burn-in is rather a form of placebo effect -- you spend a long time listening to some headphones, and you grow accustomed to and appreciative of their specific characteristics.

I have too many people who live on Long Island who tried the GH50JM Edition to think anything less than the review I wrote and those listener friends who critique them all feel the same as I do- all of them professional audio video/mixers and musicians and producers... which makes it a real head scratch-er when I read your assessment . As a matter of fact- I have an "audiophile" friend who could afford anything he wants-who auditions equipment around the world and now owns the Perfect 8 The Force Ensemble with VACs Statements and Walker Turntable- he said the GH50JM is the best he has heard in a closed back ever as well....

I stand by my thoughts and respect your assessment- that's what makes this hobby so great- there is flavor for everyone... I can also say I have read a lot of reviews I totally disagree with- for instance the Sony WH-1000XM4 received rave reviews but I personally found the sound polar opposite of what I look for in a headphone. I found many rave reviews on many highly regarded IEMs with multiple drivers very curious and a let down as well- their timing was all off for me- like so many 3rd order crossovers like B&W Speakers etc. I can go on and on- we all like what we like and stay away from things we don't. Yet the world continues to turn and blessed is the differences that make this world so colorful.

It's entirely possible the unit I got was simply defective in some manner But I am moving on to try other closed-back options for now. Perhaps when the pandemic is over I'll have an opportunity to try another GH50JM, when I'm not paying to have one shipped to me across the continent and am in less dire need for a better daily driver for work than my Teaks or V-Modas.

And ya, that's very true -- everyone has their own taste. I can't stand almost any Sony or Sennheiser headphones despite both brands receiving rave reviews across most of their higher-end lineups. On the other hand, I am strangely attached to my V-Moda M-100s and M-200s -- despite most saying they're just so-so.