Hi Sean,
No writing to the DACs is another method that can be used if you don't have any feedback. We went through all the trouble to get the spindle so it could be commanded like an axis so the axis would write to the DAC to maintain exact speed and ramp in a controlled manner and so forth. So configure to use the C Programs that do Jogs to an axis as described here. Note it describes to set USE_POS_NEG_VOLTAGE to 0 if you have a system like yours that can only use positive voltages for both directions.
To have KMotionCNC display actual Spindle Speed configure KMotionCNC | Tool Setup | Trajectory Planner | Threading as described here.