Discounts on additional items after first item purchase

I am not sure if I should've posted this here or in the sales/coupons section so if this is in the wrong section I apologize.

I am currently running zan cart 1.38 and was having difficulty figuring out how to put together a discount on additional items purchased after the first item is added to the cart.

Example:
Item A has two attributes. the Attributes are 1 and 2.
If i buy one Item A with Attribute 1 it costs 100 dollars
If i buy two Item A Both with Attribute 1 it costs 100 for the first item and the second one costs 50.
If i buy 2 Item A with attribute 1 and two Item A with attribute 2 the first Item A costs 100 but the other three Item A's cost 50 each.

Is there any add on or setting i can do to allow this?

From the way you've explained that, it seems as if the first item A is 100 and any subsequent item A, regardless of attribute, is 50.

If that's correct, why not just use quantity discounts?

If not, I recommend you contact ThatSoftwareGuy.com who is the discount specialist