12v --> 10v Nowforever D100S2R2B inverter & MKS-V-V02 CDXHCTECH board

[magicniner]

One for the electronic experts - would a pair of resistors in series across the 12V output with values chosen to give 10V at the centre tap point work? All outputs would be 10/12 ths of the input so it would track all intermediate speeds ? If so just 2 cheap components required

That's a classic Voltage Divider and Yes, it will work provided your circuit can carry enough current to deliver the signal current required (V=IR)
Do the maths in combination with the input impedance data from the controller manual.
Remember that sourcing any current from a simple resistor based Voltage Divider will skew the output, you need to know the input impedance and available current to work out the values which will safely give the best result.
Hence my suggestion of an Op Amp circuit with fractional gain.

- Nick