go try SRH840, HD380pro, DT770pro, K553, and the M-Audio HDH50/Akai MPC/Denon HP2000. All within the same price bracket, and fellow (edit: full-sized) closed-backs.
M50x gets wrecked by them all.
welp, I tried srh840 and they sound just like m50's with slight improvement on the clarity of highs. but they a very uncomfortaple to wear, and they break easily. (m50's are not hard to break too, tho)
and I tried DT770 (32ohm, because it is fair comparison) and their highs are toothshatteringly overwhelming. they have huuge peak at 10khz (or somewhere else high, i don't really care what graphs say) which cuts my ears and splits my head in half. i can't understand how people can promote them as a replacement for m50 (or how can they even pay their own money for this sadistic product. they are just painfull to listen. but i understand, it's taste thing).
also I tried:
V-moda crossfire LP which sounds like an ass. a lot of bass, and very stupid bulky bass.
V-moda crossfire M-100 which sounds pretty but has very hard V-shaped feeling to it.
AKG K550 MKII same bass ass as LP
Koss Pro4s has weirdly pleasing sound with good detail on highs (in some cases better than m50's), but a bit poor on a bass side.
Ultrasone 880 sounds like M-100. a bit more polite but still a bit v-shaped and on a bass side
Sony MDR-1a just an ass
Sony MDR-7520 have very weird unnatural and cheap sounding highs. like every cymbal is recorded in mp3 and then played along with other musicians.
Yamaha HPH-MT220 sounds cool, and weirdly cool, because very different from coolness of m50's, although i don't know how to describe it. like it is more strict and electric (yeah, every epithet sounds stupid). their highs are a bit on a harsh side, but not even close to be as painfull as beyer's.
all of them i listened with Fiio X1 and a bunch of flacs by Soen, Meshuggah and Wild Cherry
What should i try next, sensei? I'm on a quest to find a pair of closed-back over-ear headphones that sound like m50 (or better) in a twice as m50x pricerange but more durable than them. (because they have idiotic design of earcup hinges and break apart very easily)