Our Evan had inflammatory bowel disease--it manifested as an allergy to protein. Once he was on a protein, inflammation would develop over a few months in response to it and we'd have to switch proteins. After a while, novel proteins are hard to find.
We eventually went to the hydrolyzed protein foods--the proteins are broken into shorter strings of amino acids that the body theoretically doesn't recognize as proteins--but it sounds like Bobby is reacting to the HA now, as well?
Jan, you might want to reconsider a course of pred. With Evan, we had him on pred for a few months, just to knock back the inflammation. We found that if we tried new proteins and he had any residual inflammation in his intestine from the old one, it made the new intolerance develop faster. So we used pred to get rid of the inflammation, then put him on Hills' version of hypoallergenic food--I think it was called ZD. After he was on the new food, we weaned him off the pred and were able to control his IBD with diet alone. We actually fed a mix of HA and ZD since HA didn't have enough flavor to tempt him to eat and ZD had too much. That might not work for Bobby, though, if he's already intolerant of the HA.
Good luck with this! It's a difficult challenge, that's for sure!