Do the IR commands work when sending them to the sub, via IR from the front of the Nevo remote? Check this first and see if the codes are ok. Assumes your sub will receive the IR commands via line-of-sight. To test this you will need to change the NC settings for the sub so the IR will go out of the Nevo remote and not through the NC.
But I think you have a few other things mixed up.
1) An IR port on your sub is not a data in port unless it is marked as RS-232. These are two very different things. It is likely an IR port for adding a remote receiver to it or if it is labeled as IR in, to possibly connect it to the NC via a direct wire like you are trying to do.
2) If you want to try and send the IR commands via the NC and down a wire, the mini plug needs to be a mono variety on the NC. Not certain what the sub wants for the mini plug. Why are you trying a stereo mini plug? Does the sub spec this? Mono is the best guess for the sub. For sure the NC wants a mono mini plug. IR emitters use mono mini plug on the NC.
3) Using a three-circuit (stereo) plug will not work even as a data out from the back of the NC. The NC wants a 4-conductor mini plug when using the NC port for RS-232 communication.