Here are my two cents, FWIW: When you're petting Schroder, don't rub his belly. Someone (I forget whom) told me that belly rubbing is sexual in nature to cats and it arouses them and stirs up aggression. Gently give him ear scritchies but don't even stroke him until later on. I think you probably already know the other suggestion because I sound like a broken record. Can't help it, though; it works: Clomicalm. If, after you've tried everything else, he still doesn't calm down, Clomicalm works wonders. When I think of how my Specs used to fight w/Boo, it makes me sad because I didn't know about Clomicalm then. Now they sleep together. Once you get the dosage adjusted, it shouldn't be too long before you see results. My cats have not had any side effects whatsoever. Perhaps talk to your vet about it and see what s/he says.

Good luck, Moesha. I know how frustrating it can be and I also know that you don't want to return Schroeder. I didn't want to find a home for Specs either but I was at that point when I found Clomicalm.