Yes, there is no proven evidence of improvement in these DT990 Pro 250, but swapping the cable to OCC may removes phisical bariers in structure of not so perfect original cable, while use of equalizer introduces additional degradation. Additionally, original cable is 3-wires, while this OCC has 4 wires as should it be!
I play with headphones cables quite frequently and differences are sometimes huge.
Convincing demonstration might be the swapping of the cables in SuperLux HD-668B - there are shorter and longer cables provided and additional possibility to connect the headphones directly to the amp without any of these cables - difference in all three cases is easy to notice.
Edited by borizm - 2/7/12 at 6:09pm