i think what you are asking for is incorrect. First - an item as a unit - with a type, a size and a color, probably one sku also.
Your customer can order multiples of the unit - say 3 of t--shirts, L, Red
If customer wants to order t-shirt red in small, t-shirt red in med, t-shirt red in large, that is 3 separate units and requires 3 separate "add to cart clicks" to purchase all three.
First you can set your options to do what you're asking about. Secondly - it is an accounting and packing nightmare to handle your customers orders CORRECTLY.
I shop online at large and small shops, big box stores, etc and this is the way it is done. Multiples of one unique item, is okay.
multiple of items in different sizes are different selections on the cart and need to be separate line items on the invoice.
A red shirt is a different item than a green shirt it should require two actions on your customers part.
Lee
