Pros: Sound quality, price, comfort, build quality, interchangeable parts
These are not my first headphones. Over the years I had various marks and types, and even an electrostatics (Jecklin Float Electrostat).
But those are the best that I ever heard for the price range. Dynamics is incredible, they sound in a very natural way, bass is full but very fast, midrange is very clean and warm, treble is detailed but always sweet, one can listen to all types of music with the same pleasure, and without any auditive tiredness.
Of course, like with all high end headphones, it is obligatory to listen to them with a dedicated amplifier to obtain the best sound.
I use a G&W T2.6F, a hybrid chinese headphones amp, with tubes on the input and pure class A single-ended MOSFETs on the output.
It has all the necessary power to drive the Senn HD580 perfectly.
In conclusion, a royal listening.