Before I start my review, I would like to Thank AT US for providing me with a review sample in exchange for my honest opinion.You have to be living under a rock not to be familiar with ATH-M50 headphones and their latest M50x model which introduced detachable cables. With thousands of 5-star reviews on Amazon and still crowned as #1 Best Seller, you don’t have to take my word about their popularity. After my recent review of ATH-MSR7 where I discovered it being a more reference quality upscale version, it still wasn’t clear to me if these going to be an upgrade to M50x. Now with introduction of M70x model, I was very intrigued to find out how these new headphones going to sound, and perhaps wishfully thinking it’s going to be an upgrade to M50x. To my surprise it looks like Audio-Technica decided to completely rewrite the book with these headphones, to the point where everything from a design to a sound signature has been changed in this new M-series flagship model. Here is what I found.Starting with a packaging, it’s nearly identical to M50x and has the same redesigned (in comparison to the original M50) large rectangular carton box. The graphics and the entire layout of the front and the back of the box is nearly the same between M50x and M70x, with an only exception of the updated Spec and Accessories. Don’t expect to see intimate design details like those found with IM-series or CKR-series or the latest MSR7 model. Something tells me it’s not an accident those are omitted, considering M-series is geared more toward studio musicians rather than headphone listening enthusiasts. But either way, you get a great overview of the design, accessories, and the spec, and will also pick up a few hints of what to expect. Audio-Technica is usually accurate with a sound description without marketing hype, so I took it seriously when I read “M-Series flagship model, tuned for extremely accurate reproduction…”Unboxing pictures.After opening the box you would expect to see a familiar look with 90deg flipped earcups and a flat storage view of M70x (similar to M50x display), but instead you are faced with a hard shell case. Yes, finally Audio-Technica included a hard shell storage case! Unlike M50x, M70x doesn’t fold inward of the headband so your storage is limited to a flat placement with rotated earcups thus making a storage case a bit bulky. But nevertheless, I was very pleased to see a rather nice storage case instead of a typical draw string storage pouch. Another surprise was to see a molded spot inside of the case with a zippered storage bag containing replacement cables and ¼” adapter. 3 replacement cables were included, a studio 1.2m-3.0m coiled expandable cable, 3.0m straight studio cable, and 1.2m straight portable cable (my favorite). Both studio cables have a threaded 3.5mm connector to use with ¼” adapter, and all 3 cables have the headphone side with 2.5mm connector and interlocking twist mechanism. The good news, these are identical to M50x cables, the same thicker quality cables with a good durable build. No cable with a smartphone control was included, Audio-Technica made it very clear these are for professional studio use rather than everyday on-the-go use with a smartphone.Accessory pictures.The new design of M70x was another big surprise with a number of improvements and a few steps back. Obviously, we all have different head anatomy so opinions will vary. The first thing that stood out for me was a headband. It's about 2/3 of the original M50x width and has padding only on inside of the headband while outside is plastic. It looks a lot cleaner and slimmer, and inner foam padding is actually thicker and softer - a slightly improved comfort level but using padding only in the middle top while covering the rest of the inner band with plastic. I don't mind this change, and as a matter of fact it makes M70x look more professional versus M50x looking more like a DJ headphones, but I can see how the edge between plastic and pleather (or protein leather) can catch some hair.As soon as you proceed to height adjustment, you can feel a nice click action and appreciate aluminum parts of the extended piece - build quality in here is solid, no creaks or wobbling. The joint connection between y-fork and headband has been completely redesigned, allowing only 90deg rotation one way and a little bit in the opposite direction, but no longer will you be able to fold earcups inside of the headband. The only disadvantage of this is not being able to use some of the smaller storage cases, but keep in mind - M70x already comes with a nice case, so it’s not a showstopper. Also, less complicated joint mechanism means a more reliable physical design. In addition to aluminum y-fork, the back of earcups is also made out of aluminum alloy with an etched logo. M70x earpads felt identical to M50x and also have the same size, shape, and opening. Also similar to M50x, the cable attaches to the Left earcup and uses the same twist-lock mechanism and identical 2.5mm plug. One overall difference I found, and it could be a matter of personal opinion, was that M50x had a more snugly fit around my head. Upon closer examination, I found that M50x earcups in comparison to M70x have a greater degree of pivoting angle around x-axis which results in a better “hug” around my head. This could be only subjective relative to my head shape/anatomy, but I consider M50x to be more comfortable for extended period of use.Design detail pictures.I mentioned in the intro of my review that AT decided to rewrite the book on these headphones, and sound signature was not an exception. Beside the obvious recommendation for 50-60hrs of burn in before making you final decision about their sound signature, I really advice everybody to approach M70x with an open mind and understanding these are not intended to have an upgraded M50x sound, but rather a brand new neutral analytical sound signature tuned specifically for a professional monitoring. These are not fun listening headphones with a smooth warm sound and deep bass response - it's all about accuracy!!! The sound does extends pretty low and relatively high to capture a wide frequency range according to the spec of 5Hz-40kHz, but it's all about quality rather than quantity.To summarize, M70x has a neutral bright analytical sound sig with a high level of detail retrieval. Starting with a low end, it has a great extension to capture details of deep sub-bass rumble with a snappy and somewhat hollow mid-bass punch, but you will NOT feel the bass - you will hear it rather than feel it. The separation from mids is surgically clean because there is no leakage or spillage. As a matter of fact, lower mids are very lean and a bit cold. Upper mids are also thin, bright, detailed - they lack body, but very precise and analytical. Treble is bright and crisp, with a great extension, and absolutely no sibilance. To my surprise even the most offending sibilant test track in my collection was at tolerable borderline.When it comes to soundstage, I found it to be just average in width and depth, actually with more depth than width. This created an intimate listening atmosphere that helps keep a focus on the music, important for professional audio monitoring. Also, I found separation and layering to be quite good, but positioning and imaging was just average, limited by their average soundstage. I guess that was expected.I have to be honest, this is my first neutral analytical pair of full size headphones, even HP150 was more balanced, warmer, and with slightly enhanced low end. Therefore, I don't have anything to use in direct comparison to M70x. But I have a feeling a lot of people will be trying to make sense of MSR7 vs M70x vs M50x, trying to decide which one going to suite their needs better.Luckily, it's a very easy decision because there is not much of overlap between these models. If you are not looking for a critical analytical listening, and just want to enjoy a warm smooth balanced sound with some bass enhancement - M50x is a perfect choice, especially for a comfortable extended listening. If deeper sub-bass boost is not your highest priority, and you would prefer a more balanced reference signature with a nice full body sound and enhanced details - that's where MSR7 comes into a picture. But if you don't want to be distracted by a bass or artifacts of wider soundstage and actually prefer to analyze sounds or need to work on mixing/mastering of the music where it's critical to have headphones with neutral signature and close to flat frequency response - M70x will be a great choice.Overall, as much as I was missing my healthy dose of bass while listening to M70x, I suddenly realized that my focus has shifted into analytical mode where I was paying a closer attention to hidden details of the recording, little nuances of singer taking a breath, number of echo repetitions, and so on. Now looking back at a comparison between M50x, MSR7, and M70x, I can say with a certainty that MSR7 is more of an upgrade to M50x rather than M70x. It has a solid design, a great selection of accessories including 3 detachable cables, an excellent headphone storage case, and a very unique sound signature. Now I feel like these could definitely be called a true M-Series flagship headphones, while some might argue that M50x signature wasn't exactly fitted for pro monitoring purpose. I wouldn't recommend M70x for a general listening purpose, but for studio mixing/mastering and any other professional monitoring work requiring critical attention to details - these definitely deserve a serious consideration!