7i76 spindle index

I have a servo motor as a spindle. It is run off the analog spin out on the 7i76. The motor is geared 2 to 1 and I have the motor encoder is attached to ENCA +/- and ENCB +/- with jumpers W4,5,6 in the right hand position with the conversion for gearing handled in my ini file.

In order to do tapping I need to get a spindle index signal off the spindle itself and plan to use a photo interruptor on a slotted disk. This will obviously be a single ended signal to IDX+. Will this be an issue since the encoder is differential or will I need to use the motor encoder in single ended mode only?

The single-ended/differential mode select jumpers are separate for A,B,IDX so you can jumper the encoder A/B
lines for differential and the index for single ended if desired.

W6 = A MODE
W5 = B MODE
W4 = IDX MODE

That is what I assumed but I would have figured they were the other way around W4 for A etc. Is there any draw back to using a single ended index for tapping? It will not be affected by the scaling of the rest of the encoder correct?

Thank you for the reply.