Pros: lightweight, iPhone case-friendly jack, easy to drive, neutral, mid bass, soft treble; airy, musical mids; good soundstage, good with synths
Cons: skinny, non-detachable cable; slightly floppy (has lots of magnesium though), sub bass, initial ear pad comfort, sometimes shouty upper mid range
I purchased the MA900s to go along with my AKG K702 65 Anniversaries, as I wanted a headphone which didn't require amping and would be a little more musical with synths (AKGs tend to be too honest and 2D and untextured sounding with electronic and synthesized bass, and prefer instruments more). And so far, my impressions are that these are a great open-back, all-rounders for beginning audiophiles who want a headphone that goes well with almost every genre (save for bottom heavy stuff like dubstep and more mainstream rap) but do not have the amps and other equipment necessary for other open backs such as Beyers, Senns and AKGs to perform at optimum levels.
Much of my electronic music is disco, diva and deep house; and liquid funk (downtempo drum and bass), which I prefer to sound more airy, quick and upper to mid bass-oriented with emphasized vocals. The MA900s handle both of those genres admirably well and remain quick. They have a slightly rolled off, although still airy treble, which is what I prefer for downtempo music. The MA900s also handle downtempo trip hop and neo soul well with their smooth vocals and dark sound. The MA900s are overall a mid bass and mids-heavy headphone with roll-off on both the high and low end. Sonically, they remind me of a cross between a slightly rolled off AKG Quincy Jones Q701 (with its musical, neutral but lean misds) and the laid back sound Sennheiser HD500-series but without the thick lower mid bass and echoey, somewhat reverberated vocals. Although on paper it would be similar sounding to the AKG K702 Annies and K712 with its slightly elevated mid bass and rolled off highs, the MA900 is less analytical and has a more airy sound from my listening experience with less thickness.
Ear cup comfort is a little so-so FOR ME, and this is due to the fact that I have overly sensitive ears. If I shift the earcups all the way forward, my ears do not touch the driver cover padding, however the edge of the pads dig into the cartilage behind my ears, causing them to become sore. I find that shifting the headphones slightly back to where the driver pads lightly touch my ears is the most optimum position for comfort. I usually hate having things touching my ears and creating hot spots, but it over time it ceases to become an issue, and my ears quickly settle in. Will most people experience initial comfort iffiness like I will? No, but for those who have sensitive ears, you might want to keep this in mind. The MA900s do not have the roominess of Sennheiser ear cups, but they don't have those echoey vocals and head clamp, either.
The MA900s are fairly light and lack that bulky feel that AKGs and Beyerdynamics have. Which means they don't feel overly cumbersome and are ideal for longterm music listening sessions, but this does mean their build quality is unfortunately rather on the floppy side. They don't have that chunky, substantial feel like Sennheiser HD518s or HD598s have. However, the MA900s have a large amount of magnesium in their build, comprising the driver back grill, the yolk and the yolk arms attached to the ear cups. The MA900 does look and feel premium, it just does not feel rugged or chunky.
Another small complaint I have is the cable, which is hard wired, skinny, long, terminates to a standard 3.5 mm jack which oddly has a plastic barrel surround. On a positive note, the jack is fairly slim and will easily fit in an iPhone case. And that ties into my final point. The MA900 has a nominal impedance of 12 ohms, and although they benefit from amping, you don't need one to get them to sound good (unlike AKGs). You could run them off a potato if you wanted to. The phone case-friendly 3.5 mm jack and included snap-on stereo plug that seems like an afterthought hint to me that the MA900s are not mainly targeted towards the audiophile who has tons of high end gear and likes to swap for higher end cables, but to the average consumer who wants a no-fuss, elegant, relaxed, dynamic-sounding headphone.
If you have a good amp and want a drier, more analytical sound, I would suggest instead checking out the new AKG K612 or Q701 instead. But if you are a beginner with open backs and do not have an amp to work with, I cannot recommend the MA900s highly enough. Just make sure to treat them well and not be rough with them. They retail for 300 US dollars, but you can get them for less than 200 on Amazon. A great headphone for around 200 dollars.
Update: The ear pads, which were initially too pokey and hard have since broken in over time, and have become much more comfortable. I expect this comfort to get even better over time.