A client has a special group of customers, aka G1, who automatically get an initial group discount, aka D1. Additionally, they can get two more discounts based on quantity.

One of the quantity discounts, aka D2, is given in addition to D1 if the customer purchases quantity X.

The third discount, aka D3, will be given to a subgroup of G1 who meet an additional quantity purchase requirement that is greater than X.

How can this pricing be handled in Zen Cart?