Have you asked him why he zones out with you? You've said that he sympathises, apologises and then does it again - but does he know WHY? Does your voice remind him of someone else in his family?
This is barely related but still - years ago I was given a black wig, bob style and I wore it around, pretending that I'd had my hair cut and dyed (it's VERY different from black bob!) My Dad refused to speak to me, couldn't even look at me - because with that hairstyle and colour, I reminded him very strongly of an ex-colleague who he hated, and he couldn't dissociate it from the image I was presenting. I never wore it around him again, it was too upsetting for us both!
So, that was just to illustrate how sometimes things can trigger a response, even though it's not directed specifically at you - but he would need to know why he's having that response with you. It might not be something else, it might be you - but how can you know unless he knows and tells you?
Another thing - you're suggesting he is completely disengaged from you, not looking, not listening (except he is because he's parroting stuff back to you, or knows the set responses that you are expecting) - have you tried something like touching his arm, taking his hand, putting a hand on his shoulder - engage a different sense, it might help him to respond better to you.
Some people react better to different sense stimuli - another good one from my parents (hopeless communicators) - I did a test on them and it turned out that my Mum was primarily an auditory processor, while my Dad was primarily a visual processor and had very little auditory capacity. Mum always said that Dad never listened, Dad always said that Mum never saw things his way - well no! they didn't. Mum would have done better leaving notes for Dad (or using semaphore/sign language) and Dad would have done better to speak to Mum more rather than using visual cues and expecting her to respond to them.
OR - he could just be fed up within the marriage and just CBA, but that one really is quite hard to address. :(