Hi caringheart:
Welcome to the forum. I'm sorry to hear about your dilemma but maybe some of our experiences will assist you in hopefully rectifying the little lad's problems. I have been working with a cat now for 10 years who has IBD plus a couple of other hangups. Basically I was very fortunate after the 2nd vet I went to had run a battery of tests she mentioned IBD along with major liver problems, and her recommendation was home prepared meals for Missy. I worked with her for a year until the vet was injured in an accident and I had to find another vet. After going through all the paperwork from the other vet and the work she had done the new vet recommendation was raw food. He also said that commercial pet food was not suitable especially for cats, and he wasn't fussy on it for dogs either. So I went from home prepared cook type to raw, and it's meant for a lot healthier and happier Cat, not to mention peace of mind.
I would strongly recommend looking into alternative food types preferably raw for your young guy. I see you're going to be seeing a new veterinarian make sure you feel comfortable working with that person and the person is willing to talk alternative food types, and has some knowledge in it. Remember when you are talking to veterinarians the majority of their knowledge of nutrition is extremely limited normally supplied by the pet food manufacturer in order for them to promote their product down the road.
I will supply you with 3 websites that I find very useful, and they are as good as any to start with. I wouldn't be the least bit surprised if you switch to raw or something as good, that both your problems will be over in a couple months. The switching him from commercial food to homemade is going to take time and plenty of patience. In these 3 websites that are mentioned they have ideas to make it easier on the switchover.
http://www.holisticat.com/en/
http://www.catinfo.org/
http://feline-nutrition.org/index.php
I think you'll find if you do some research into food types that it will give you a win win win situation. 1 peace of mind, 2 less stress on the wallet, and 3 a lot healthier and happier cat.
Hopefully there is some information in this that will be of benefit to you, and do keep us informed of your decisions and how things are going.