"(I don't believe in burn-in mechanically with dynamic drivers)"
 
I don't believe in anything with regards to audio, but I accidentally discovered that some headphones do require burn-in.
 
I had a pair of dynamic driver headphones that I received right near release.  I listened to the out of the box, and I immediately disliked the harsh upper midrange, and the lack of bass.  I started thinking about what other cool headphones I could buy if I sold these.  So, my bias was definitely towards wanting them to continue to sound bad.
 
Since they were just released, I wanted to help the community by reviewing them, and I had just read a spate of reviews with burn-in times specified.  So, with relief, I put them in a drawer connected to a music player for 24 hours and then listened to them.  They sounded much better - contrary to what I wanted.  So no placebo, no expectation bias and no cool headphones bought with the sales proceeds.  I put them back in the drawer and they continued to improve a little over another couple of days, but the 24 hours difference was the most significant.
 
There is also no possibility of "brain adjustment", because I did not listen to them very much during the first period, and not at all while they were in the drawer.
 
So - not through any desire of mine, in fact the opposite of what I "wanted" - all the usual explanation of burn-in were debunked.

One can hear different from day to day as well. You might have been tired or something.

David - to put what you are saying in a different way " that is only one data point " and of course, scientifically it does not prove anything.
 
But tired wasn't the explanation - I listen to music all the time, and listened to speakers and other headphones before and after those sessions.
 
Note that there are easy scientific explanations for burn-in.  If you wear a pair of shoes for 100 or 500 hours, they fit differently.  It's not controversial.  I think that burn-in is controversial on head-fi simply because people do not want to wait 4 days to evaluate their headphones.

Perhaps. Audio is so damn subjective as it is so I prefer not to draw any conclusions. 1 opinion among many you know..

Uh.. so you rated these well but then proceeded to give them 2 stars? Why?

2 stars = 4/10 = bad. Yeah, these are BAD headphones. Right.

may be you got a defective unit or something .. and you say no sub bass, harsh upper mids ?? I dont agree with you at all !

The headphone is being compared to more refined, more expensive, and higher tier headphones, so I can understand them sounding a bit meh in comparison, although I'm personally not of a fan of either the HD 800 or K701 in terms of sonic signature; those headphones are clearly a league or two above the MA900. I do have to agree that the MA900 does have a slight lack of coherence and do lack sub bass. The upper mids I did find them harsh/grainy on some systems, other systems I found the upper midrange and lower treble fine. I think the MA900s are good headphones, but they aren't great headphones for the price in terms of sonic ability.

if you think ma900 is not great headphones for the price, then before that you might have to add more overpriced headphones for that list.. including hd800,hd700,hd650,hd600 .. yes those headphones are more refined but anyone could also argue those headphones dont have the the sonic ability comparing with their price too..

Yeah sorry guys, but I just think you can do better for the money in regards to sonic ability. Also, the only headphones I compared them to was the K701 and HD600. They can be bought for about the same price or cheaper on the used market like I stressed. And imo are much better headphones for music. 

I respect your review for your tastes - except a) Comparing Used and New prices is silly.  If they were the same, there would be no difference in price.  And b) Price structures in UK are different. And c) If you didn't burn them in for 24 hours, you don't know how they sound, as I previously explained.  Neither of us "believe" in burn-in, but burn-in doesn't care that we don't believe in it.