I have the same problem and have tried many different things too. All though I haven't had much luck, but maybe they will work for you.
I read an article that said cats spray when they become depressed or anxiety-ridden because of change. And believe it or not they have an anti-anxiety medication for cats in a cream form that you rub into the inside of their ear once a day. I haven't talked to my vet about this yet.
Are your cats neutered/spayed? That is supposed to eliminate their desire to spray outside of the litter box.
Apparently, cats HATE walking on aluminum foil. We have 2 cats who will stay 3 feet away from it, but one cat who will even sleep on it. You could try putting the foil around the sides of the litter box where he is pooping.
Cats don't like the smell of cirtus either. I've read that you should put half a lemon in the area where they are spraying or try some citrus scented spray. The lemon thing works pretty well, but it is a major hassle to keep buying and replacing the lemons, especially if it is happening in a lot of areas of the home. I haven't been able to find cirus-scented Febreeze or carpet cleaner though. If you do let me know!
I found a cat repellent spray. It keeps the cats away from the area because they hate the smell, but humans can smell it too, and it is disgusting. And my cat just ended up getting used to the smell.
I think keeping a litter box upstairs is worth trying, and other than keeping your cat confined to one area, there's not much else you can do. Hope some of these ideas work for your kitties!!