Some versions of the Allen and Heath GS-R24 documentation mention that the analog module is a 1 in / 1 out 37 pin d-sub connector. Custom cabling has to be made for this type of connector.
I've found that the analog modules that are currently shipping contain 4 in / 4 out 25 pin d-sub connectors. These 25 pin d-subs are standardised Tascam 25 pinout. As such, they don't require custom cabling.