I can't specify a percentage off defined products when ordering 10 items or more in magento.

If you use Product Promotions extension and can't set up a percentage off only defined products and only when a buyer ordered more then a specified number of items, please, perform the following instructions.

Open Promotions→Shopping Cart Price Rules.

Conditions: Set a condition that triggers the rule only if the cart contains 10 or more of SKU1 and/or SKU2 combined.

Actions: Set the actions to send a discount only in case SKU1 and/or SKU2 are in the cart.