Hmmm, it really concerns me about the vomiting...I've been sitting here thinking about it. I know you're a poo inspector like me, how are his poos during these times? Does he vomit right after a meal or later? Was it w/ all flavors? Does his tummy make gurgly sounds ever? I think you did add a digestive enzyme, right (otherwise, you might think about it)?
I'm trying to think of this tummy infection someone posted about a while back and can't recall now...I think some bloodwork confirmed some things, but I just can't recall the details. Did his bloodwork show anything odd?
I did try HK for the boys - this was quite a while back. I got some samples and they liked it twice - so then I bought a $44 bucket of it...and they hated it after the next meal or two. I don't know why. It seems like such a good food. But maybe try to sample it for a GOOD two weeks before you buy one of those big buckets.