For best performance from your access point, you will want to give the access point a wired connection back to the FiOS router. Otherwise, you will be bottlenecked and subjected to the quality of the wireless signal from the FiOS router.
As for setting up the ZyXEL device as a repeater, look at the user guide for the device on how to set it up manually. WPS or Wireless Protected Setup isn't supported even on the FiOS routers with the button.