You can run these drives by configuring the PMDX-424 to supply +5V on
its COM outputs of the motor connectors and wire the COM to the input
for +5V on the G214.
The G214 need access to both +5V and GND if you plan to use the ERR
(fault) and FS (full step) outputs. This can be accomplished by connecting
the GND of the G214 to the Lgnd on J12 of the PMDX-424. If you have an
older PMDX-424 this terminal may be labeled PCgnd.
Regarding resolution, you should keep in mind that micro-stepping does
not achieve full torque exactly at the desired location and you may have
trade offs between resolution and torque at rest. Extra microsteps can
help significantly with smoothness, but cannot magically produce extra
resolution that your motors lack the torque to support. If you are caught
between a rock and a hard place, there are stepper motors that use
400 full steps per revolution, which would double your resolution.