For singleaxis FW, use Singleaxis-V208 and for DualDC use DualDC-V2004 or later. The motor wiring is different between the FW's.
In VSDEPI the DualDC channels are in pairs of XY and ZA where DualDC drive is connected to X or Z port. So if you set X & Y as individual (sinleaxis FW) axis, then should put DualDC on Z with VSDEPI jumpers inserted. For slave axis, just configure Mach to output identical step signals to both axis.