I know you have a couple of threads around here and I may have missed something somewhere but has your vet checked for parasites, bacterial infections (like salmonella, ecoli, which is completely possible to get from kibble somethimes), blocked anal glands? Having blood in the stool is definitely not normal and while I do totally agree that this diet change is in order, I would also want to check on those other things.
Also, here's a link that may be helpful though I'm sure you have already looked this stuff up, I'm just grasping at straws here...
http://m.cat-world.com.au/?url=http...16608/blood-in-stool-after-negative-test#2631
Also, here's a link that may be helpful though I'm sure you have already looked this stuff up, I'm just grasping at straws here...
http://m.cat-world.com.au/?url=http...16608/blood-in-stool-after-negative-test#2631