The XB1000s have a great emphasis on sub-bass, can be EQed to XB500 mid-bass levels, have a huge soundstage, and are semi-open.  There are large air ports on both the top and the bottom of the drivers, and as a result they leak more than the XB500/700s.

To get the best out of them, yes, but I wouldn't say an amp is outright required to enjoy them.  I'm using them with just computers/iPods with software EQing and I'm already impressed.    I have a Z02 and it didn't change the sound of my XB1000s any more than I could through EQ.  Any...