How does your husband express himself? Like would it be easier for him to journal or write his thoughts in a letter and give that to you?
My husband's default coping mechanism with uncomfortable conversations is to shut down, get defensive, put up walls, stop all feelings that he can. We worked hard on this in the early part of our marriage, but it got bad during the A. And he's tryign to work his way out of it.
Our MC is working on imago, where he works on hearing and validating - rather than feeling like he has to "respond" to what I say. By putting it into his own words, sometimes that alone makes a lightbulb go off (and vice versa). Being freed of having to react also puts him in a different role than feeling like it needs to be a turn-based I say-he respond - i respond - he respond, etc. type situation.
That you're trying is a step in the direction. This isn't a sprint, it's a very long marathon.