One_Eyed_JackalA lot of people seem to have this question.
The answer would be "depends on your definition of well". It will drive the 6xx to enjoyable levels (70-100 db) without a problem. It will not drive the 6xx (rated at 97 db SPL at 1mW) to the threshold of pain i.e 120db before clipping (their specs say 42mW at 300 Ohms while keeping the THD+N <= 0.1%) but why would you ever want to listen to music at that level? Around 10-20mW of power is sufficient for *most* human beings to enjoy their music on the 6xx.
This is good enough for you but probably not good enough for your cat.