I have schizophrenia, I am currently unemployed and have been for some time. My wife does think I have ADHD, but I have not been diagnosed because in a brief discussion about it with my psychiatrist, he said with the antipsychotics I'm on I cannot be given a stimulant, which is the standard treatment for ADHD as I understand it. I often struggle with the stress of emotional conversation with my wife and often shut down, I have gotten better at it because I want to support her, because I feel like I do not do enough and being listening is the least I can do. And as I have gotten strong in my capacity to listen, I have then got even stronger. But that is like going to the gym you need to get into the habit before you see continual returns of more fitness/strength.
I found it hard to talk to my wife because I am the least contributing member of our relationship, but also, I always felt like I was wrong (and often am). I don't get angry; I have had that in check since my 20's but I did shut down because I could not face my wife. Perhaps the answer for your husband is the same as it was for me. Don't to try and get a diagnosis of ADHD which is every expensive, but rather get him to talk to a psychologist, where he can talk without judgment about his feelings, about why he gets angry and shuts down, about the possibility of ADHD. And talk about how he can better communicate with you. I know with the Medicare rebate, and seeing a consultant psychologist we were only out $60 per session, which is not chicken feed but is much more doable than an ADHD diagnosis (also if you are in Qld or SA GPs can now diagnose ADHD). And if you are near a capital city, I was a bus driver for 10 years. Its cruisie, fun, the bus companies train you and it pays pretty well.