I bought a "serial" cable from Amazon. RS-232 on one end, and DVI on the other. Directly from the PC to the DCX. Works great.
At one time, I had bought an adaptor to go from RS-232 to USB, but the drivers kept crashing and were very buggy. I tried a couple different types, but they all sucked. I'll give you mine if you want.
The DCX software comes from the Behringer site and is free.
Bob