Perhaps a dumb question but are they center panned (or mono, i.e. talking over each other) or is it split left ear/right ear when they come through the headset?

That tracks. As a teacher I sometimes find myself conversing with multiple kids simultaniously as well. If it's nothing too deep that requires full focus, it works. (Though I do find it tiring and avoid it.)

I'm a native English speaking pinball freak living as an expat in a German-speaking country, and I find myself often listening to English speakers on the train, while also carrying on a conversation in German .. and I have observed that the same part of my mind that can handle multi ball-pinball events, where during a pinball session multiple balls are in play, 'feels' active.

Its a kind of context juggling mechanism in both cases, and it feels like the same mental muscle being exercised in both cases.

I wonder if there is a worthwhile experiment to be conducted wherein an EEG'ed pinball player gets to play pinball with easy multi ball targets, while also listening to German and English speakers, and then passing a test at the end of it .. because I sure have been preparing for that kind of scenario lately ..

You're using one of the streams for yourself. :P

Listening and responding are likely pretty different mental activities

I def process more than I want.

Its def a spectrum.

In the easiest look at people like me who complain very quick if something is wrong like to warm to cold to sweaty etc. and others not even ackknowliding it at all

Absolutely. Take a look at "unconscious perception".

Many dj mixers offer the option to split the main mix to one ear and the cue’d track to the other, i have never been able to mix like that, only with cue on headphones and main mix out in the room/monitors. Weird

Not reading out loud, but I've caught myself a few times on reading and not processing that, because I was thinking about something else. Like I still did the reading, but straight to /dev/null of my brain

I experienced this too, when I started reading out loud more. At first, it was just that my eyes would scan ahead a bit from what I was saying, to help me get the right emphasis by knowing where the sentence was going. It felt like I had "handed off" saying the words out loud to a "subroutine", so my attention could be on what I was reading. Then that "readahead" extended to a whole sentence. And at that point it was like I was so far ahead of what I was saying that I had time to think about it a bit. And then at some point it was like the "reading the words" part got handed off to a "subroutine" too, so my attention could mostly stay on whatever I was thinking

Sometimes I read a book out loud and think about something completely different.

I wonder if reading aloud might be like walking. I can be walking and speaking to a person at the same time.

This is something that has been studied and is apparently more common when reading out loud. I have this as well. I can read to my kids and at the same time plan the upcoming day. Pretty neat!

Also explains why we like music with two simultaneous distinct sections (bass + the rest). One without the other doesn't feel as complete