Just picked up some of these. They come with a detachable cord. Was wondering where I could pick up a higher grade quality replacement for the stock one. The catch is it only plugs into on side, not like the HD600s or higher models (two sides). Who makes a cord like this?

I'm getting a set of Sennheiser HD 515. Which amp would match up well with it? Looking at spending around $200-$300. For now it will be matched up with a cheap DVD player, later on my Rotel RCD-1070 CD Player.