Pros: Powerful bass, Impact, Speed, Imaging, Detail, Comfort
Cons: Too Bright in the upper treble, Recessed Midrange
I've owned this headphone for years, and I cannot say that about any other headphone. I've compared it to headphones costing multiple times its cost, other "supposed" EDM cans, and other Ultrasone headphones.
The Pro 900 is special. It's the bass, which when properly amped, goes very deep, very low, and sounds powerful. This headphone also has some very good impact, slamming nice and hard on electro house tracks. The bass goes deep, but it doesn't sound uncontrolled or boomy. It can sound boomy without an amp, though.
Speaking of amps, I would HIGHLY recommend the Matrix M-Stage. I have the second version, HPA2, and it pairs extremely well with the 900s, and the other headphones in the Pro line. Amplification is important here, to hear that deep bass extension, and keep things in control.
Okay, so it has great bass. What else?
Well, the headphone is fast. It can keep up with fast beats without having too much linger. This is important for Electronic music, which can get very fast.
These also have great detail. If you've never heard Ultrasones before, it's a safe bet you will hear things in your music you haven't heard before with their extended highs and very clear sound.
Now the mids. They are pretty recessed, meaning they sound further back in the music (quieter). Even though this is true, it is obvious... If you're going to boost the low end and the high end, the middle part is going to sound less "boosted". The mids are still very detailed, just not emphasized much in the overall sound signature. That's okay. You don't need forward mids for EDM.
These are very comfortable. As the pads break in, they soften. The pad on top is very comfortable as well. I can wear them for hours with no problems at all. I actually love their design.
Furthermore, these are built like tanks. You'd have to try really hard to damage these.
Positioning? You want the back of your ears just grazing the back of the ear pads. That's what works for me, at least. It's effortless to get a good fit, once you adjust the size to fit your head comfortably.
These have nice imaging when you get them positioned right. You can hear sounds from lower left, upper right, etc. It's a very interesting experience and something I have found the Ultrasones to excel at vs other brands I have tried.
I think that's about it. These headphones have given me probably 1,000's of hours of listening enjoyment. I love them. Though they aren't perfect, they offer a unique sound signature that no one else seems to offer. And if you love it like me, that makes them very special. High recommendations if you are an EDM listener.
Don't hesitate to add a comment if you love your 900's, or if you have any comments or questions.