Currently there are two configurations of conventional 6 pole XLRs. The NEUTRIK 6 pole XLR meets the industry standard according IEC 61076-2-103. Nevertheless NEUTRIK offers both types of 6 pin configurations. The standard NEUTRIK 6 pin has a black insert - the insert of the non-standard configuration is gray.

The difference in the part #s is the additional “S”:
NC6MX - standard 6 pole male XLR cable connector, nickel housing, silver contacts
NC6MXS - same product with non-standard pin configuration