The IE 900 is a headphone designed for maximum audio quality, period. 
Sennheiser delivers in that department,

The Sennheiser IE 900 is an in-ear headphone designed for users who care about amazing sound reproduction above all else. 
It’s two in-ear monitors connect to an audio-only cable.
 
A good seal in your ear canal eliminates the need for potentially music-altering active noise cancellation.

The Sennheiser IE 900s are Sennheiser’s latest flagship audiophile earphones that showcase the very best in audio technology. 

For the IE 900s, Sennheiser has introduced new innovative techniques and improved previous designs to provide a set of earphones that delivers a listening experience without compromise.

The IE 900s feature Sennheiser’s proprietary 7mm X3R transducer, a unique triple-chamber absorber system and their ultra thin XWB driver design. 

Combined together, these innovations deliver a