Sony sent us the MDR-1000X for this test, which is comparable in terms of pricing to the PXC 550. The MDR-1000X is a bit heaver though due to its fairly large earcups covered in leather. In practice you don't really notice the extra weight. We felt that these headphones were very comfortable, even when worn for a longer period of time.
The buttons are all on the left earcup and not always easy to find by touch in our opinion. Sony has also separated Bluetooth and noise cancellation. They've done it by adding a separate power button, that can be held down to set up a Bluetooth connection. Of course this can be done through NFC, as we'd expect from Sony. Above it is the button that enables or disables noise cancellation. If you hold this button after enabling noise cancellation, you'll start the so-called Optimizer, which will optimize the noise cancellation based on your surroundings. A third button is used to control Ambient Sound, which has two settings: Normal and Voice. The former does not block sounds from for example traffic, while the latter does the same, but then for voices. If you want to pay attention for second, you simply cover the right cup with a flat hand, after which noise cancellation is temporarily disabled and the volume is also lowered. The volume levels can be controlled with gestures on the right cup, but you can also use it to skip songs or pick up calls. All these features only work when the headphones are turned on.
We've got nothing but praise for the audio quality of these headphones. It's clearly the best, together with the Sennheiser and AKG headphones, however the Sony headphones have a bit more power and therefore sound a bit richer. Details are excellent, just as the balance, except for the overrepresented low tones when noise cancellation is turned on. Do note, our positive judgement is only true when the MDR-1000X is actually turned on, with or without noise cancellation on. It sounds much worse in combination with the Huawei Nova that we used to test the headphones when it was turned off. There seems to be some sort of amplification inside of the headphones. A good DAC might lower the difference. The cups of the MDR-1000X dampen a lot of noise by themselves, but it's good to know that the noise cancellation also work well. It's not as good as the noise cancellation on the Bose or Sennheiser, but it comes very close.