Hmm, well I thought the picture with the controller interface and the Green and Yellow wire connections was the DSP. But it could be that this board is a front end for the YAKO which may be the "big brain". However the steppers are connected to the yellow connection pads as I understand this, so I guess the A+ A- etc is either a buss connected to the "green side" or then the D-sub cable is connected to the "green side" of the circuit board that the steppers are connected to. It's not easy to distinguish the different cables on the "green" side but there is a Red,Blue,Yellow cable but no Green....
But I guess if we had a look at the "Yellow" side of the board we could see how many wires connected. From the picture it looks like 4 (by counting the soldered stubs going down to the circuit board) but it may not be that there are 4 cables connected on the other side.
As for me, I'm just trying to figure out how this is working, simply by studying you're pictures and the data sheets on commercial stepper motors, so please take my subjective evaluation as it is; Established from the high north by studying the different "bells and whistles".
If however there is a manual available I could read, I would be happy to study it for all of us which is potentially interested in a 4th axis. In case, please feel free to drop it in a email to me (PM me and I'll send you my email adr). Is "YAKO" the controller name, I would start searching for this on the web so we hopefully could get to the bottom of this
K