Complex eCommerce question – multiple choice issue

Hi,
I am trying to set up a small business but it has been difficult to find a solution for my somewhat (but not completely) unusual store needs. I’ll outline the issue here:

I have 9 items. They all cost the same. A pack of 4 costs a fixed sum (less than 4 individual items). A subscription to receive 4 every week for 4 weeks costs a fixed sum (less than 4 4-packs). Someone buying a 4-pack or a subscription must be able to choose which items are included, including the option for more than one of each type.

Examples:

• Mr X orders a single box of item A.
• Miss Y orders a 4-pack containing a box of item A, two boxes of item B and one box of item C.
• Mrs Z orders 4 4-packs, each with different mixtures of items

eShop seems like a great plugin but doesn’t allow me to set up this way. Does anyone know if this is possible in ANY WordPress plugin? Does anyone have any general comments on my intended setup?

Many thanks in advance for any feedback.

Paul