custom fields with individual quantity selector & just one "add to cart"

[graphos]

Hi!!

I`m trying to achieve this in the category page:
I have a product (bottle of wine) that can be packed in boxes of 3, 6 or 12 bottles. Every box has a different value. I need that the client can add to the cart the desired quantity of boxes, and make some combinations. i.e 1 box of 12 bottles, 2 boxes of 3 and 4 boxes of 6. So, I need that every variant has its own quantity selector (+,- controllers), but just one "add to cart" button.

Product 1 -  box w/ 3 units:$930 (+)(-) ;  box 6 units: $1500 (+)(-) ; |add to cart|

Second: I need that the total price be updated in the category list. It happens only in details view by now.

Thanks! Any help will be appreciated

In the attached you can see what i need.

Joomla 2.5.4
Virtuemart 2.0.6

You can take a look to what I've done by now
http://www.sibwana.com/vinos/index.php/arma-tu-caja

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