My 22 year old son is visiting while on break from school. For the last 5 years, his music listening has been through headphones only. I've made a couple of very startling observations. He cannot tell the difference between M3, M5, M50 and M100. They all sound the same to him. He also cannot perceive soundstage depth through any of my speakers.

I conclude therefore his continuous headphone listening has damaged his synapses responsible for certain auditory cues.

It can't POSSIBLY be that brain damage runs in the family.

Likely similar to the brain damage that afflicts both of us, Craig.

Kids don't pick up such cues without prompting.

I know some that even in musical/dancing training have no rhythm at all.

It typically would be best to ask him to relay his best/favorite headphones to you. Depending on his likes\taste of sound stage amount of Bass.

He could probably recreate a similar near field setup using one of your bookshelves. Maybe fun? To see how different your tastes may be?
When I was a kid we all thought Boomboxes or an old 2 channel hooked up ghetto surround was the greatest thing.{multiple old speakers everywhere}