Hi there !
I have been reading this thread for a while now, and I wanted to thank you all, because it helped me to make up my mind one year ago and buy the MM400s
First of all, I just wanted to say that these cans DO sound fantastic, and I can guarantee that they are worth the money !
I had the opportunity to compare them to their main competitors : the B&W P7, the Oppo PM-3, and the Sennheiser Momentum (over-ear). To my mind, they were the ones that sounded the best, followed very closely by the PM3, which are excellent headphones too. These are two very natural sounding pair of headphones. Nevertheless, I felt like the MM400s were a bit more extended than the PM3s, and I prefered their more intimate soundstage.
If someone needs a comparison between the MM400s and the V-Moda XS/M80s, I could probably help because they were my previous cans, but as English isn't my main language, I'm afraid of not being able to explain the sound difference in a very detailled manner.
As many of you did, I also wanted to state that these headphones really OPEN-UP and gain a lot from being burned-in ! I was extremely disappointed when I took them out of the box and listened to them for the first time, but now I'm extremely happy with them and it's not because I became accustomed to their sound at all ! I remember that the sound was very harsh, completely deprived of bass, and I that couldn't listen to them for more than 10 minutes without hurting my ears. I downloaded pink/white noise and let them burn-in for several days and the sound really flattened ! After that, the sound kept getting better as time passed. I remember though that there was a period during which the highs were veiled, but it was nothing that the equalizer of my DX50 couldn't fix