The reference voltage for the DV8825 is 0.92v, measured from the trim potentiometer to ground.
The reference voltage for the A4988 is around 0.55v, measured at the test pad on the driver.
The 8825 upgrade is great on X and Y, and you can already see the improvement in detail. I also double the resolution again by using stepper motors that need 400 steps per full 360-degee rotation (0.9-degree per step), instead of the 200 steps (1.8-degee per step) that the standard steppers do.
I hope everything is woking for you now. Happy printing!