You should have the ability to add a discount on a product line item instead of a blanket discount on the total amount. If certain products are/are not subject to certain discounts, you have to create a manual line with a -$00 amount currently instead of being able to add a % or $ off discount on the line item itself. The one discount per subtotal total really screws things up if you’re adding shipping to an invoice and try to use discounts % how they currently are, it also discounts your shipping.