Hi Timewellwasted,
Sound is very subjective & personal, as you spend more time on headfi, you'll find a lot of heated debates on sound preferences & the like which can be very unproductive & unhelpful as those who are fans of certain brands will only suggest those, nothing else.
As said, what's important is to know what you like where sound &/or music is concerned, it's among many reasons why people get into this very interesting past time.
Though what not many bring up is how music makes them feel, feeling sound is just as important if not more than hearing sound but it is the combination which determines how well it fits for you.
Only you can answer your own questions you put forward which is why it's not only important to know your sources very well, with those same sources being of quality.
Then with these two points in mind, you can experiment listening from not only different headphones, IEMs, players, amplifiers, etc, the list goes on.
As experimentation continues, you will find what appeals to you & go from there.
Almost ironically, I have the MSR 7 & Meze 99 which I got in reverse order to how you phrased your query.
I stress these are all different headphones, so in a sense, in my subjective personal opinion, they can't really be compared in the same catergory.
Also, aside from Noise Cancelling (which is the selling point) the WH 1000 X M2 has a built in amp which subjectively again, is close to on the go reference level without any added gear, eg, portable amp, etc.
So in brief, keep in mind, this is my personal subjective opinion are as follows :
MSR 7 is a good musically responsive headphone which caters well to quality sound in all genres with equal measure on the go for an affordable price.
Meze 99 Classics are as the name suggests, leaning towards classical, jazz, etc but handles anything with good bass response very well, eg, metal, rock, edm, etc definitely better than the MSR 7, with a sound which leans towards warm & smooth, almost refined but with enough space overall to better immerse the listener. It is one of the few headphones at this level & price which require minimum 'burn in' of 20 hours for that supposed resolving effect though Meze himself recommends 40 hours.
There is some truth the sound changes but it is tricky sometimes to say how this sits subjectively, once again, only the listener can answer that question.
They are perhaps the only 'fashion cans' which can perform but that's just my personal subjective opinion as they're definitely out there to be noticed.
Once you listen to many headphones & IEMs, you'll realise there is such a thing as what some refer to as 'house sound' or distinctive to a particular brand & this more often than not causes much heated debates in the forums as some will prefer one over the other &/or say only that sound is superior over others, case in point, any of the headphones made by these first three letters, sen.
Personally, subjectively, I am not convinced this is the case & I steer clear of this example on a combination of principle & having experienced many others which appeal to me more.
There are also a few other brands who have a sound which doesn't appeal to me personally or 'loses' me after a time.
One last thing to note, even for those brands I don't like as a general rule as I've just outlined, I can agree on a technical level they sound good but to the level others rave about?
Definitely not.
