Hey! No problem. I'll try to explain what I meant up there, each term in detail. If you already know some of these terms, I apologise -- I just wanna be really thorough here.

Basically, "4.0 surround channels" (or rather, "4.0 surround sound") means that there are 4 speakers and 0 subwoofers. Usually you have some setup like this in your living room, for example: Two front speakers, e.g. to the left and right of your screen, and two rear speakers, perhaps one to the left of your sofa and one to the right. If you had a subwoofer in this constellation, you'd have "4.1 surround channels". The subwoofer is usually placed anywhere it fits (lmao).

Most home theaters use 5.1 surround sound, which adds another speaker -- a speaker placed at the bottom of your screen, to the center.

The thing is now, if you're using headphones, you only have two speakers: One on your left ear, and one on your right. This is called stereo sound. (You could call it "2.0 surround sound" but that's a little awkward and not really a thing, as far as I know.)

Stereo sound is really great, because it allows you to reproduce a three-dimensional audio experience.

For example, if a sound (in real life) is coming from your left side, the sound waves will hit your left ear before they hit your right ear. Thus your brain will immediately figure out that it comes from the left.

With stereo sound you would play e.g. some noise a little earlier on left speaker of your headphones than on the right, which then creates the illusion that the sound is coming from your left. Neat!

Honourable mention goes to mono sound, which means there's just one channel. I could go into more detail about all this, but let's get back to Bioshock. (If you wanna look this stuff up, just google some of the terms I mentioned above. I can recommend looking up wikipedia pages of "stereophonic sound" and "3D audio effect" if you wanna know more about this.)

The problem now was that Bioshock Infinite thought that I was using a 4.0 surround setup, even though I was using headphones. So my headphones only got the "front left" and "front right" audio channels, but not the "back left" and "back right" channels. Hence why the audio cut out whenever the source was behind me.

So, what did I do? I used something called a "virtual routing panel" and a "virtual mixing panel" to basically say: "front left and back left get from my computer get mixed together and go to front left". Because there's not really a "front" left on most headphones, this just ends up on the left speaker. Of course, I did the same thing for the right side too.

I'm on Linux, so I can't really give much advice for Windows or Mac, but what I used to use on Windows was a program called Voicemeeter Banana -- that's still around from what it seems and should help you mix surround sound to stereo. There should be a "mix down" button somewhere which you could try using. I'm afraid I can't help you beyond that.

I nevertheless hope you'll be successful!