In terms of sonic performance, the Pro DJ100s sound dry, analytic, and lacking in deep bass. Pendulum's "Salt in the Wounds" should make your head thrum, but the Koss can't reach down far enough to do it justice.
The lack of low-end detail also has a distancing effect on the soundtracks to music and games -- it's not as bad as listening to a TV from another room, but rather a hollower sound that what some might also call "airy" and lightweight. Considering the Pro DJ100s are pitched as DJ headphones, this top-heavy mix is certainly a misstep.
As befits a pair of studio cans, Koss is able to illuminate the darker corners of a recording in terms of surface background vocals and instruments. The sound is never irritating, though, and even steely keyboards are kept in check.
Are these true DJ headphones, though, or just gussied-up consumer cans? They'll do the job if you want a pair of headphones to excavate more detail than your stock earbuds, but their bass-shy response limits their attraction to serious DJs.