You guys aren't giving the ma900s enough credit. In headphones, like with many things in life, price ≠ quality. I own several headphones, including ma900 and 650hd; the ma900s are one of my most used, and I agree the hd650 are going to be a living hell for people with an oval shaped face where the cups sit on your jaw bones. Even if you reduce the clamp force its going to be bothersome.
Sound wise i feel they are very similar. They are both warm with a big soundstage and headphones are only 1 link in the chain. If you use flac music with a good dac and a good amplifier, the ma900s trump the 650s imo, simply because i can actually wear them for more than 5 minutes without feeling miserable, and because they have a very nice warm and pleasurable sound that you don't get with many headphones.
Thing is, lot of people look at the ma900 low impedeance and think "oh these are easy to drive, i'll just plug them into my computer's front panel audio jack!!" (which is one of the worst places to plug them in) - and even though they still love the sound, they wait until they get more expensive headphones to buy a dac/amp and then feel like the ma-900s are a lot worse.
the mdr-z7 is about 200$ more retail compared to the hd650 and it is closed. Personally i found them too boomy, though probably because they are closed. If you find the 650s uncomfortable and want a set of cans that sound similar but are enjoyable to wear too, then the ma-900s are the best choice. Like I said, people with more ovaly faces with low jaw joints will probably find the 650hd uncomfortable, but since the ma-900 has round ear cups and is light as a feather with very mild clamp force, they should be perfect.
I'm not going to beat around the bush here. The MA900 is a good headphone. But its just that, good, not great. On the other hand, the HD650 is a great headphone. Also, just so you know, price is not always proportional to quality.
When I first got the MA900 I was impressed with them, very much so actually. I liked their warmth and their midrange presence. After being exposed to higher-end gear (and purchasing some), as well as upgrading my source and amp, it was clear to me that the MA900 is massively flawed, thus my harsh criticism.
I don't get your third point. So what has that got to do with me? My MA900's were plugged into a Hifimediy Sabre DAC, after that I upgraded to the Aune T1 with an Amperex 7308 tube ($70 tube), and now they're being powered by my LH Labs GOv2, which I consider the best of my three sources by quite a large margin. The fact of the matter is, however, every single source I plugged my MA900's into, they were grainy in the lower midrange and sounded thin - despite their warmth. This is an issue that was discussed innumerably here. Once you hear that grain, you can't un-hear and its very bothersome. Then there's the thinness. I don't understand where its coming from particularly, and given the headphone's sound signature it shouldn't sound like that, but it does. As a whole I feel the sound lacks authority and thickness. I think that at the price the MA900's are currently retailing for which is around $200+, the Fidelio X1's are a more viable option, as well as DT880 Pro. Both the aforementioned headphones are a step up from the Ma900's IMO.
"If you use flac music with a good dac and a good amplifier, the ma900s trump the 650s imo" What?! Would you mind telling me what you're plugging them into? Because throughout the entirety of my MA900 and HD650 ownership, never have I got the slightest doubt regarding the HD650's superiority - both technically and musically. I've had my MA900's since late 2013 now, and my HD650's aren't even a year old.
FYI, I still use my MA900's on a daily basis. I like them but I do recognize their very noticeable faults. I use them for gaming and their fantastic soundstage and accurate imaging render it an excellent gaming headphone. The added midbass also helps.
If you like your MA900's that much then by all means, no one's stopping you from enjoying them. But you can't deny that they also have some major flaws
Lastly, the differences FLAC makes are minuscule, but thats a whole nother argument. Your information is extremely misleading. Please do not parrot around what you read here on the forums. Try things for your own self and make up your own mind.
As always, YMMV.