My wife was eating a slice of pizza and our beagle full on attacks our pit/boxer for getting to close to the food.

Beagle is a 6 year old fixed male from a hunting line and the pit/boxer is a 9 month old unfixed female.

He drew blood on three places on her face before I stopped it.  Luckily I stopped it before she started to fight back.  I have a feeling her bites would be a lot worse than his.

I feel like some of the issue is we put down a much bigger dog lab/wolfhound mix two months ago and it's changed the pack dynamic.

Anyone have any success convincing a beagle food isn't worth dying over?

Beagles not the brightest bulb in the package.  It may take an ass kickin' to convince.

Beagles are wonderful dogs and on average have the intellect of a 9 year old human. Unfortunately they are a nose and stomach with 4 feet. The only downside to them is that they are very food driven. As in they would truly eat themselves to death if given the chance. They are the ultimate pack animal which is why they make such wonderful pets because they adopt you as part of their pack. I suspect that you are correct in that you changed the pack dynamic in your home and she’s out of sorts. Unfortunately they are so food driven, they were bred for chasing down food after all, they are ridiculous if ever started on human food. Best just to cut off their crack and let her begin the withdrawal process. She’ll still love you but hate you for it.

You just taught your beagle that it can kick your pit/boxers ass and that you will protect the beagle from reprisal.  This is the same reason some small dogs become agressive small dogs.

"Anyone have any success convincing a beagle food isn't worth dying over?"  I'm sure your pit/boxer could have done a good enough job doing that itself.
"... and it's changed the pack dynamic."  You are right, and now you need to let them reestablish what that dynamic needs to be.  As long as you and the human family are on top and they aren't literally maining or killing eachother, let dogs be dogs.