Actually yes I had one little guy that was chronic with the liquid poop he had IBD, although he is no longer with me, here is what solved his.......RAW! Just good old fashioned raw chicken. Now this was long before I found this board or ever knew a cat could be diabetic, so didn't have Dr. Lisa's raw diet to follow and make my cats food myself back then so with Sebastian what I did on the suggestion of a nice woman that bred Rag Dolls (Bastian was a rag doll) was I took Fancy Feast (I think, one of the 95% meat canned foods its been 10 years so memory fails) Chicken canned food and added 20% fresh raw ground chicken meat to it. Now because I'm paranoid when it come to my babies I did buy chicken breasts and then grind them up in a food processor when I did this as I don't generally trust what else they put in the commercial ground meats.
But with Tibbs you might want to look into just buying already mixed up raw food for him. I believe Feline Pride has some fairly reasonable priced raw the they ship frozen in big tubs. that you just thaw out and serve. I know we also had a little girl at the shelter where I volunteer that also had a dog with IBD and I believe they added raw meat or switched her over to a raw meat diet and she also improved drastically.
You might try before buying offering him some bites of raw chicken and see if he'll eat it that way, if he will then move on to giving him about 20% of his food as just plain raw chicken and if that goes well then try switching him over to a completely raw diet, the other plus to feeding a raw diet is that its just about the lowest carb diabetic cat food out there, and as close as we can get them to what they were meant to eat in nature short of going out and catching live mice for them.
Mel and The Fur Gang