I'm going to have to second Craigster75 on this.
The pro 900 shouldn't by any means be compared to the sig DJ. The pro 900 has a higher distortion as well. XB500 wins the award for most bass, more than Q40, pro900 and M100.
Just to compare distortion here:
Pro 900 Measured (Note distortion)
XB500 (Most bass quantity, but bass bleeds into mids a bit, sounding a bit...