The xb1000's have more sub bass than any other in the xb line, more so than even the LCD 2 even, but it oesnt really have that mid bass punch that the xb500 and othe bass oriented headphones have.
Songs like cookie monsta's ginger pubes or dead prez hip hop which have long rumbling bass lines make the xb1000 nearly rumble off your skull with no eq. But songs lacking strong sub bass notes will seem like xb1000 has weaker bass than other phones you may have used.
The way the xb500 and xb1000 handle bass is totally different, xb500 is more in your face, its the closest you can get to car subwoofer bass, the xb 1000 is tighter more refined bass with significantly less bass overall but dominates in how the bass is presented in terms of quality and in my eyes is the undisputed king of sub bass