Are the grounds 2,4,6,8 internally connected ie equal on the cncaddon ?

Ie can I connect like this

PoKeysCNCaddon (10Pin)   MCA808 X1 (DB9 male)
3  DIR   --------------------------->    1 DIR+
2  GND   -------------------------->    6 DIR-,
                                                  7 PUL-,
                                                  8 ERC-
5  STEP --------------------------->    2 PUL+
1  ENABLE --------------------------->    3 ERC+

The reason is that the nr of connections increases quite a lot, If I need to do extra lines 7,8 for each of 4 drives.
I am running out of motor data lines on the 25 pins connectors out-of-controller.

Yes, GND pins are all internally connected on the PoKeysCNCaddon.