Pros: Fantastic bass, treble and soundstage. Quite comfortable. Easy to drive.
Cons: Vocals could be more prominent. A bit bulky. Not the lightest headphone.
These headphones are a huge step up from anything I've ever heard before.
The only other well known headphones I've listened to extensively are the Sennheiser HD 202 and the Logitech UE6000. Compared to these headphones, the sound quality of the X1 is better in every way.
In my opinion the Fidelio X1 has a truly fantastic bass and treble response. The bass impact of these headphones during action sequences in movies really adds a level of immersion I've not experienced before. I'm also hearing a lot of details in music I previously did not know studio recordings picked up. Sometimes it feels like sensory overlord since I'm not used to listening to this level of detail. I also find that the excellent bass and soundstage makes Jazz sound especially good with these cans.
My only complaint with the X1 is that I sometimes feel the vocals in music and speech in movies are not as prominent as I would like. These headphones are also a bit bulk and slightly heavier than ideal in my opinion. However, the comfort of the ear pads are great.
I use these headphones with the Audioquest Dragonfly and I find this combination to be a great match. If you want to know which DAC/amp to use with the X1, check out the results of a survey I conducted:
These results contains feedback and recommendations from over 30 Fidelio X1 users on the different amps and DACs they have used with this headphone.