Can The SX Be Converted to an S Drive?

No. The SX cannot be "dumbed down" into an S drive, so as to be controlled by a Step & Direction signal.

The SX can generate step-and-direction signals to send to another drive. The E-AC is an inexpensive basic stepper drive, good up to 3.5 Amps-peak. The Zeta8 is capable of 8 Amps-peak.