HunterlTurnerI've owned both. Compared to the Philips Fidelio X2, the AKG K7XX ...
... has less mid- and upper-bass.
... has a more-realistic, balanced, revealing, neutral sound - especially noticeable with instrumental/orchestral music.
... has less clamp, and bigger ear-cups (Some would say that the K7XX's camping force is too light, and its ear-cups are too big. The X2's camping force and size of the ear-cups will be near-perfect for most users.)
... feels a bit flimsy with its almost entirely plastic design (The X2 is mostly made of metal parts and feels much sturdier - but only slightly heavier.)
... has a single-sided mini-XLR connector (The X2 uses the more-common, less-expensive 1/8" stereo 'aux' cable.)
... has a plastic, self-adjusting headband mechanism which can break more easily than the X2's stretchy, cloth-based, self-adjusting headband.
Both headphones have a fairly wide sound-stage. The X2 wins on durability, but the K7XX's sound is superior.