before you can setup any of the drivers you need to sort out your config file. if you are still getting errors about SQL then even your config setting to use the PAM driver is not being picked up. Are you sure you are editing the correct file? what is the the location of the file, something like /path/to/roundcube/plugins/password/config.inc.php are you sure that is the config path that the epel Roundcube package uses? I have never used that package myself so I have no idea.
