Cat and Irritable Bowel Disease

I'm hoping someone can help with this problem for one of our cats who is
diagnosed with IBD. We have tried MANY remedies to control his hunger
and his unexpected bouts of diarrhea. He has been and is currently on a
special diet of food called ""Natural Balance" mixed with "NaturVet"
Digestive Enzymes Prebiotics and Probiotics. We also provide a B12 shot
once a month per Vets orders. We have tried Slippery Elm and some other
homeopathic herb mixed with his food for several months to no avail.
Occasionally he would have a diarrhea bout after he got into something
he wasn't supposed to but lately, he's still having bouts after we
assured he isn't getting into any other food. He's losing weight and
appears frail, while constantly hanging around the kitchen for scraps to
fall or to be fed. He's such a lovable little guy who I hate to see
suffer with this disease.

Can anyone offer some insight and/or suggestive assistance to help
before this thing takes him to far?

Thank you