Have you ever tried to work on changing his thinking to how imperfections are actually a good thing?  I like things to be “just that certain way” but what helped me a lot was this story that’s become a favorite of mine.  Whenever something isn’t to my liking, I try to look at it from the story’s point of view.  Maybe it could help Emmett too?
Imperfections—
An elderly Chinese woman had two large pots, each hung on the ends of a pole which she carried across her neck.
One of the pots had a crack in it while the other pot was perfect and always delivered a full portion of water.
At the end of the long walks from the stream to the house, the cracked pot arrived only half full.
For a full two years this went on daily, with the woman bringing home only one and a half pots of water.
Of course, the perfect pot was proud of its accomplishments.
But the poor cracked pot was ashamed of its own imperfection, and miserable that it could only do half of what it had been made to do.
After two years of what it perceived to be bitter failure, it spoke to the woman one day by the stream.
“I am ashamed of myself, because this crack in my side causes water to leak out all the way back to your house.”
The old woman smiled, “Did you notice that there are flowers on your side of the path, but not on the other pot’s side?”
“That’s because I have always known about your flaw, so I planted flower seeds on your side of the path, and every day while we walk back, you water them.”
“For two years I have been able to pick these beautiful flowers to decorate the table.
Without you being just the way you are, there would not be this beauty to grace the house.”
Each of us has our own unique flaw. But it’s the cracks and flaws we each have that make our lives together so very interesting and rewarding.

My girl would lose her mind if anything splashed or spilled, or if anyone/anything bumped her glasses. There was no way to stop or end her epic meltdowns at that point. They lasted as long as they did. Poor babe. In the end, we can’t make them not be who they are, not care about what they care about. In many other cases, upset over other things, we were taught to intervene, to shorten the meltdown by redirecting her thoughts with behavioural intervention. We could lead her to do silly things, perform some tasks very quickly we ask her to do to prove that she could still listen, was still in control of herself even though she was upset, and that she was a very capable girl. Then praise her to the heavens for doing what we asked and reward her with something she likes. It’s called behavioural therapy and it’s a very effective technique. It takes time and patience, and the higher functioning kids catch on often and can start to do it themselves when they get upset. It’s very cool to see it in action. Doesn’t work in every situation, of course. Nothing does. But I wanted you to know there’s hope. There are ways.