[Franco]

I think you're not understanding the difference the mid information on a stereo recording and the central image of a stereo system, this is why I went back and edited my last reply to say:

"(not talking about accessing the center frequencies that can be focused on a M/S matrix..)"

When you split a stereo on it's mid/side, the information that you get when decoding the mid channel is mono, and you can hear this on headphones as well; the center image in a system happens when the frequencies coming from the left speaker overlap the ones coming from the right, and this is why it's refered to as an "image" because it will be different for example, if you have the speaker too close to each other, and too far away from each other (unlike decoding a stereo file for a m/s matrix, the outcome is based not on acoustics); part of setting up your speakers in your room involves finding the optimal placement of the speakers relative to the room.

You're talking about the mid information of a stereo file - that is a mathematical computation, you're right about that. However, this is not what we're talking about when talking about the center IMAGE - that is an acoustic property that depends on placement of speakers and signature of a room. It will vary depending on several factors, unlike the mathematical outcome of decoding a stereo file into its mid/side information.

Can you isolate a stereo track's center information? SURE - hit "Mono" on your monitor controller.

Can you isolate a stereo track's center image? NO, you can only change it by repositioning your speakers.

I don't think you're talking about the mid channel when you originally said this:

"Your brain misinterprets what the mix really sounds like when you're listening in cans (in particular, changes in ambience and the center channel's relative volume)."

There's no chance in "ambience and volume" when decoding a stereo file to its mid/side; you get a change in this by skewing the center image.

You still don't have an accurate statement about headphones.