Pricing - Modifier sertup for Promotion

Hi Pricing gurus,

Can you please help me with the below requirement.I have below scenario to setup a modifier for a Promotion:

If customer buys 1 Qty of Item A he can get a discount of 10% on 1 Qty on either or Item X,Y,Z . If he buys 2 Qty of Item A he can get a discount of 10% on 2 Qty on either or Item X,Y,Z

Lets say price of Item X =$100 and Y= $200 and Z=$300.

If he buy 1 qty of Item A,X,Y and Z then he can get discount on ItemZ i.e $30.

If he buys 2Qty of A and 1qty of X,Y and Z. then he can get a discount on Item Y and Z. i.e $50. (10% on Y and 10% on Z).