When you say the "enabled" value is NO, do you mean it has a red "X" next to it? If so, and if you are looking in the "plugins" tab of the "Control configuration" dialog, then just click on the red "X" to make it a green check mark. Then click on "OK'. Now it should be available in the "select motion device" dialog.
That said - to make things easier why not clone one of the stock PMDX profiles as a starting point? They already have the basic configuration settings configured. Including having the PMDX plug-in enabled and selected. Or are you taking an existing profile and trying to change the motion device to the PMDX-411? if so, never mind :)