The other portion of the cable is for communications between the box and the TV. Check out KeyDigital for their cables, they are quite a bit less than the Pioneer cables, but still pricey.
www.keydigital.comAlso, sometimes you can remote place the box in a room behind the plasma and run analog video from your equipment to the box. I don't know what your application is, but I thought I would just throw that out there.
Matt