What is this input for on my RCA cable?

Yeah, that's just for a digital optical cable so that you can also send sound to a home theater system or surround sound headset but still have audio going to the television as well.

I did some research on this, I have found that the black port is a digital audio port, this allows you to connect your console to a sound system. Here is a link that you can look at. Hope this helps.

Link:
support.xbox.com/.../connect-sound-system

Both the HDMI Audio and Optical Audio is set to "Stereo Uncompressed" in my XBOX Settings Menu.

Yes, I have tried connecting the Sound Bar to my TV. I don't have an Optical Input on my TV, so I used the Red / White RCA cables. The Sound Bar does not work from the TV - because it is not on the same HDMI input.

(I have 7 inputs on my TV: XBOX One is on Input 7, and my cable box is on Input 8. The RCA Inputs are on Input 4.) When I connect the Red / White RCA cables to my cable box though, the Sound Bar works perfectly.

This is what is confusing. HDMI sound and RCA sound is coming fine from the cable box. But, only HDMI sound is coming from the XBOX One. The Sound Bar is silent.

Use the 3.5mm jack just as Eggs said. VGA inputs normally don't use RCA inputs for audio, they use standard PC 3.5mm inputs because they're intended to be used to connect to a PC. You will need a RCA to 3.5mm adapter in order to use your cable with your
TV. Make sure the adapter is female RCA on one end to male 3.5mm on the other. It should look something like

this.

Connect it just like a PC in the diagram on page 19 of your manual.

Ok, yesterday night, thinking about the problem, I came to a possible conclusion.

Maybe the problem is not the headset itself but the red and white RCA cable that comes with it, the one with the green output at the end.

I came to this conclusion because everytime I try to reproduce sound with that cable (Xbox or TV), it came only on the left side of the headset. But when I put them into my computer without the RCA cable, by putting the 3.5mm green cable and the USB, it
works just fine.

'Cause I tried everything that came with the headset: the speakers work, the USB works, the 3.5mm green input works, the pink one I haven't tried yet but I think it's ok, the red and white RCA cables work. The only thing remaining that made me think of this
solution is the green output on the RCA cable.

What do you think? Could be the solution to the strange problem, just the green output on the RCA cable that's broken?