The power of the Amulet lies not only in protecting against damage from a specific type of magic but also in providing 50% increased defense against creatures of that race. For example: Chaos Drake against a Titan. The Chaos Drake will deal only half of its normal damage to the Titan because it has a Chaos Amulet. However, if the hero controlling the Chaos Drake has a Ring of Minor Negation, the Chaos Drake will deal full damage to the Titan.
1) The ring only helps the wearer, not their army.
2) The ring ignores the amulet when using magic, not physical attacks.
P.S. I know what the amulet does.

Барон "Vampires"
Отдай свои прошлые сны,
В сомненьях себя обрети,
В бешеном танце душа кружится!
Не думай, что будет потом,
Здесь и сейчас мы живем,
Стань хоть на миг сам собой, слышишь!