(Glad you're sticking around!)
Dude, that's fucking UGLY! That M42000 or 556SD held up like a damn champ though! At first I wondered, "why the fuck did he put up a picture of a bunch of worms in that blast chamber?" Then I saw what they were, never seen that before. I wonder how big of a fire they had to light under AAC's ass to get any repair work done, and how long that took?
OP, I'm assuming you're using a Saker and if that's the case the Trifecta is hard as hell to beat. Also, the mount isn't compatible with unlike calibers. So that safety is built in. Why not use the Trifecta?
I pretty much have dedicated cans to my rifles. I have a multi use can that never gets used, they seldom work as well as a dedicated quality rifle can does. Only one or two share a can and a couple share three cans. My biggest concern is actually putting an AAC 5.56 can on the wrong 5.56 rifle. See, AAC mounts wobble like a motherfucker, so short of "fixing" them, best bet is to buy a bunch, find the right ones, send the rest back. What happens is each can will require specific mounts --put 'em on another mount and they'll wobble like hell.
So what I do is mark the two 556SD's with a pink paint marker "M4 1" and "M4 2" and then the cans are marked likewise. It gets worn off and has to be reapplied from time to time but it works very well. The SDN6's were bought at different times and one has more wear than the other so it requires no marks. Or put 'em on opposite shelves. Just come up with a system to keep 'em apart.
As for your question about an SOT doing the work, no, that's not required. ANY shop can do the work, however, you MUST be present while the work is being done. You cannot drop it off. So schedule a time, after hours is when I schedule laser engraving through the guy I use, and just chill and watch him work. But boring out a can, that sounds tricky to me and keeping the runout dead on would have to be a pain in the ass. Better to get another can and another mount and just keep on keepin' on. They don't call us "stamp collectors" for nothing!