AUS Controller observed an apparent incorrect path flown by an aircraft assigned the CENTEX Four SID discovering similar sounding fix names on the SID likely caused the confusion.

Narrative

A SR22 received the following clearance from AUS Clearance Delivery: AUS CWK4 TNV MLU. I RADAR identified the aircraft; issued a climb; and then cleared the aircraft direct to ILEXY Intersection to 'intercept and resume the CENTEX Four Departure'. Some time later I observed this aircraft far north of the assigned route of flight; and far past the ILEXY Intersection. I advised the pilot that he had overshot the assigned route; and I issued a new heading to join the CENTEX Four Departure. The pilot insisted that he had dialed-in the correct 'NAVYS Intersection'; and it was at this point that I realized what had happened. There is a TNV (Navasota Transition) on the CENTEX Four Departure; as well as a NAVYS Transition. Pilots often confuse NAVASOTA with NAVYS due to the similar sounding FIX and NAVAID Transitions on the CENTEX Four Departure. This issue has been previously reported. I contacted ZHU and advised them of what had happened; and switched the aircraft once I observed that he was turning back onto the proper route of flight. Such a simple fix... just change NAVYS Fix and/or Transition to a different name.