It is different by each application of equipment
Encoder solution is different based on product series, it can be affected to position accuracy. And if user of existing Ezi-SERVO series , it is  possible to have lack of torque by operating speed  with using of  S-SERVOII.
There are some difference as below specification table, Please be well- informed of specifications ,after that please to do replacement through verification with the equipment install test.

1. Encoder resolution : 10,000/20,000/32,000[ppr](Ezi-SERVO), 4,000/ 10,000 [ppr](S-SERVOII).
2. Product Line Up : Ezi-SERVO’s max motor size is 86mm / S-SERVOII has a max 60mm
3. Motor output torque : Ezi-SERVO is 40V / S-SERVOII is 24V
4. The difference of I/O signal : refer to the following images