Just to clarify...

The difference between a regular cable and a null modem cable is that the TX (transmit) and RX (receive) pins are swapped:

Regular cable:
Pin 5------- Pin 5 (Ground)
Pin 2------- Pin 2 (RX)
Pin 3------- Pin 3 (TX)

Null Modem cable:
Pin 5------- Pin 5 (Ground)
Pin 2------- Pin 3 (RX->TX)
Pin 3------- Pin 2 (TX->RX)

IMPORTANT QUESTION:
Why don't you already have the null-modem cable that came with the player?