I've owned the XB1000, XB700 and XB500. I use(d) them all with my O2amp.
The XB1000 lacks bass, and is bright (they have 2 peaks in really bad spots). I returned them, they are quite terrible.
XB700 brings you back the sub bass and a bit of punch and less fatigue.
XB500 has the most bass but is quite muddy/boxy.
The XB700 is my fav, it really sounds like a cleaned up XB500.