I think you will need to add another calcuation:
EliteTotal = ([ItemCatName]=='Elite Series Cases')?[TotalPrice]:0
Then you can set the discount rule to be based on the EliteTotal Column Total instead of the entire cart.
The second discount rule would be:
Trigger = SubTotal of EliteCaseQty > 0 : Calculation = Flat Rate $12.50
(Both would also have the discount code trigger)