products with complex attributes

Greetings,
I have been trying to find a shopping cart solution that will allow somewhat complex product listings and I can't seem to figure out which combination of software and add-ons will allow what I'm looking for.

As an example:

SKU #01 - T-shirt - XXL - Green - 10 in stock
SKU #02 - T-shirt - XXL - Blue - 12 in stock
SKU #03 - T-shirt - XL - Green - 5 in stock
SKU #04 - T-shirt - XL - White - 6 in stock

I've tried both Zen Cart & OS Commerce so far. Can anyone tell me what combination of software & add-ons would allow me to list my T-shirt on one product page, with smart options.

Choosing XXL should not allow White as an option (it's only available in XL)
Choosing XXL, Green should show a picture specific to the options chosen.
Choosing XXL, Green should decrement the stock of only the XXL, Green.
Choosing XXL, Green should send me an order with SKU #01 as the product/model.
Choosing XXL, Green should independently set the final price. (XXL might be extra, Green might be discounted)

So far, the only way I've found to accomplish this level of control would be to list my T-shirt as four separate products, each with its own product listing. Is there a way to do this that would appear to the customer as a single product with several options, but appear to me as distinct SKU?

I'm just getting started with this project and there is an overwhelming amount of help available, but I've had no luck in homing in on this specific issue, so any assistance would be greatly appreciated.

Attribute DEPENDANCY is not available in zencart, and nor is it available in most other opensource platforms.

The reason is that it is not only very difficult to code in this dependancy, but that every user has different (unique) requirements. No single (generic) solution can be built.

I have seen examples of sites that have managed this, but it has required a complete overhaul of the way the software handles attributes, and it is clear that in these examples, a whole new attributes system has been written by a very skilled coder.

Stock By attributes may help you, and I have heard that you can get some way forward with the attributes grid module.