It could be that the additional pins are not jumpers, but are instead reserved for serial terminal access to the drive's MCU.
If you have a multimeter, disconnect power from the drive, remove all the jumpers, and determine which pins are grounds (by measuring the resistances between each pin and power ground). Then power up the drive and measure the voltages at each of the remaining pins.
It would seem reasonable that no output pin would be adjacent to a ground pin, as this would expose the drive to potential damage from user error. Knowing this, it should be easy to infer which is the TX pin and which is Rx.
