Vasco:
Read up on brains. I don't have the v.2, with the built in analog inputs. My dspmc is the older version, and I use a PLC. The brain in Mach3 reads the "address" of the analog input, and activates the appropriate OEM code for Mach3.
On my mill, the plc address for the Feedrate is 28,682; the OEM code for the brain is 821.
Rapid override address is 28683; OEM code for the brain is 223.
Spindle percent override address is 28684; OEM code for the brain is 74
You must put a formula in the brain, to achieve the correct value.
John