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

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

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!

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.

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?

Absolutely. Take a look at "unconscious perception".

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