Cat food for cats with sensitive systems

I was wondering if anyone has tried blue or blue buffalo cat food and what do you think of it? I have a cat with a sensitive digestive system that throws up pretty often. I have tried different foods, the lately of being purina one for sensitve digetive systems, and he throws that up, too. He is a healthy and active cat, but just has that one particular problem. All my cats go to the vets regularly for their checkups and immunizations,and he healthwise checks out fine. I have one cat who craves greens, and was going to go and buy him some "cat grass". Will this make my other cats digestive problem worse if he gets ahold of it and eats it, too?