Proper e-collar training does not involve just putting it on a dog and waiting until he does the wrong thing and pushing buttons. This is a communication language that he must first learn without distractions and you must know and understand the dogs drives and what stimulates him and what will disengage him. This particular dog is not so much engaging in a dog fight to prove dominance, as the dogs are more cat size and he could kill them in less than 5 seconds. Proper training would lead to respecting you and your commands being more meaningful than carrying out his intention of killing the little dogs. You must become more important to him than his "dogs are dogs" instincts.
SSA is seen even in 2 spayed bitches or 2 neutered dogs. Or with one intact and one not.especially SSA that's hormonally-driven.