Dediğiniz gibi yapdım Php 5.1.6 sürüm şu şekilde ekledim php.ini ye

zend_extension_manager.optimizer=/usr/local/Zend/lib/Optimizer-3.3.0
zend_extension_manager.optimizer_ts=/usr/local/Zend/lib/Optimizer_TS-3.3.0
zend_optimizer.version=3.3.0a
zend_extension=/usr/local/Zend/lib/ZendExtensionManager.so
zend_extension_ts=/usr/local/Zend/lib/ZendExtensionManager_TS.so
zend_extension=/usr/local/ioncube/ioncube_loader_lin_5.1.so
zend_extension_ts=/usr/local/ioncube/ioncube_loader_lin_5.1_ts.so

service httpd restart diyip php -v dediğimde ioncube görünmüyor ama