First,you can not be immute to phys and magic dmg but you can absorb magic dmg.Absorb give you an extreme leech if you have the right amount.For physical,you can't not be immute to this dmg but,if you have the right combination of dr and resist,you just take a minimal dmg.
Secondly,tha max dr is not 100% the max is 75% (the game can not handle more,because 100% is immute).But for a good range put 175% because some people reduce your dr.
Hint:you can change the game stats of 75%dr if you open the .mpq files