Does the player keep rebooting only when this questionable serial cable is plugged in?

If so, you could try disconnecting certain wires. The empeg uses only pins 2, 3, and 5.

Pin 5 is ground, pins 2 and 3 are receive and transmit. Swap 2 and 3 back and forth until it works. (One way is crossover or nullmodem, the other way is straight through.)

More details here.