So relieved that you have a workable diagnosis! I think Beau may know something about the kibble and is trying to tell you - it may be a NO-GO until his tummy settles down. I agree with an earlier post that soft, moist food may be the way to go until the pred really takes hold and calms things down. Canned, poached, slow cooked, whatever it takes to establish the one protein source and then someday reintroduce kibble one kernel at a time. May take weeks or months. I have a cat that had all the symptoms but no confirming test results of IBD/pancreatitis. He ate Wellness canned turkey for a year and we managed to get his vomitting down to once a day unless he ate dry food which would result in an automatic regurgitation. Fortunately the bloody diarrhea cleared up almost immediately, but it took another couple of years for his stool to take any sort of form. We didn't get to the turkey right away - we spent an obscene amount of cash trying all sorts of food in an orderly and patient manner before hitting on the turkey.
Let Beau tell you what is going to work. If you let him, he will tell you. Sending calming thoughts to you, Robin and healing thoughts to Beau.