what is the best mixture of icing(store bought) to 1 box cake mix when making cake balls.
Some would say none at all! I'm one of those. I usually use liquor of some kind, sometimes some flavor extracts and chopped nuts and/or dried fruits (these last soaked in some kind of liquor to plump them up). I LOVE putting peanut butter and some chocolate in them, even if the coating is chocolate as well. If you like the kind of cake balls made with icing, it's more a question of your experimenting and finding what you like, because there is no standard recipe, sorry to say, but many people think that icing either makes the cake balls too sweet or makes the cake too gummy. It really is a question of personal preference. You might make several kinds and run a taste test among your customers/family members to see what goes over best.
Before you add anything, test it to see if it needs it. If it rolls into a ball and seems to stay together enough to dip it, you don't have to add anything. If it needs something, start with a few tablespoons of icing (less if using anything liquid), mix it in, test it, and go from there until you get the consistency you need.