I can empathize with you; I do hope you're able to find some relief.
My treatment was basically a targeted form of Cognitive behavioral therapy.
The first big hurdle was to learn that I had developed 'toxic hopefulness' regarding the behaviors of others: I had taught myself to eat quietly (because as a kid I learned that was the morally correct thing to do), and so I believed that because I could do it, it was reasonable to expect every other person in the world to change like I had. This is why the sounds of the city -- sirens, cars, crowds -- didn't bother me, but a single person eating did: because I had attached a moral judgement to 'correct' eating as a child.
Now, when the whole world didn't change to eat quietly like I did, I developed deep-seated moral indignation, which I covered with anger (I am very much a 'flight' person in life, except for when my misophonia triggers, and I have an emotional reflex to 'fight').
And because I was embarrassed about that anger, I added a layer of anxiety, where I was hyper-vigilant to sounds that might set off a misophonic response, which, in turn, made me that much more susceptible to people eating, or anything that could sound like someone eating. It turns out the first quarter-second of most sounds (opening doors, engines starting, boots stomping, etc) can sound like the crunch of a chip to a brain that's anxiously awaiting eating sounds.
So, if I had to boil my therapy down to a few points (and for reals -- I'm not a therapist, this is just my personal experience) it was:
1) come to terms with my toxic hopefulness and accept that there are entirely predictable ways in which the people will never change to accommodate me.
2) learn skills to manage the emotional reaction to hearing a triggering sound. For me, this came down to variations on telling myself, "This activity is natural. It is okay for people to make noise while eating" while imagining a triggering situation. I started really simple, for seconds at a time, before building up to more intense imaginal situations.
Those two combine such that it took a stronger sound to 'trigger' my misophonia, and when triggered, I developed skills to managed my emotional reflex, which in turn made the hypervigilant anxiety about getting triggered go down, which made it harder to trigger a response, which meant the skills I learned were more effective, and so on in a self-healing cycle.
Hope that helps a little.