We ship wine bottles in quantities of 6 (thats the amount of bottles that fit in a box). The customer can choose any combination of wine bottles (red, white, sparkling etc) as long as they are ordered in quantities of 6, 12, 18, 24 etc. And as you say, it will be based on categories. In this case the root category will be wine.
Thanks for your reply. Do you offer a module that adds limits and multiples to a combination of products? So the customer can mix and match products with a minimum of 6 bottles and in multiples of 6.