There is a lot to process in your statements. First of all, loss of hearing is a journey. Now you have me wondering if the volume I speak is appropriate because I only have partial hearing in my good ear. The other one is totally deaf. As an experiment, have him read a sentence or something without the hearing aids using what he considers a normal volume. Then have him read the same sentence with the hearing aids inserted in what he considers a normal voice. See if there is any difference. If not, then you can rule out the hearing aids being the problem if he speaks the same either way.
Perhaps he just yells sometimes as a long term habit from his pre-hearng aid days.
It is hard for a person with good hearing to understand, but my hearing fluctuates, and maybe it is more noticeable to me because I only have one ear, but for example if my sinuses are the least bit clogged my hearing diminishes. Does he have allergies or sinus issues?
Some hearing aids only increase volume and are not great with quality of hearing even with adjustments. Maybe if his volume is too high, he feels he has to match it.
Also make sure the aids are situated correctly in the ear. Generally if they are too far in there will be feedback, but if they are too far out, hearing might be diminished. There is a sweet spot where it is just right.
When I let people know I do not hear well, they start yelling, and that helps me not at all. I just need for them to speak more clearly and enunciate their words so it does not sound like mumbling. Perhaps he yells because he thinks by doing so, it will make you speak more loudly or clearly. Who knows?
I have no clue how bad your husband's hearing is with or without hearing aids, but hearing impairment of any kind puts you in a whole new world. Hearing aids are a wonderful tool, but they do not provide what is referred to as "normal". It is more of a "new normal" or an adjustment of what our normal used to be, if that makes sense. His new normal with the hearing aids may make it more difficult to actually hear himself so he is floundering from the loud speaking habit you say he had for years to the softer speaking volume because he can hear better with the aids. Whether you have rechargeable batteries or regular batteries, they begin to wear down during the day which also makes the hearing gradually diminish.
One last suggestion. Why not develop a hand signal between the two of you. You can wave your hand down like petting a dog (lower your speaking volume) to let him know he is speaking too loudly, or raise the hand up (like raise the volume a little). Don't laugh, because I know it sounds like training a puppy, but it will prevent the constant need to have the same discussion over and over with him about how it is hurting your ears when he yells or how you cannot hear when he speaks too softly. It also might help him in practice to learn habitually how to speak at a pleasing level.
Like I said, hearing loss is a journey, and it not only affects the hearing impaired person, but sometimes their family and friends as well. I hope some of this helps.