The Stone Edge Order Manager (
www.StoneEdge.com/OrderManager.htm) would give you a couple of ways to handle that. The simplest would be to set up individual SKUs for each quantity. In the Order Manager, you would configure each of those SKUs as a "kit". Kit A would consist of one unit, and Kit B would have two.
Example: You sell bottles of something in single bottles, carriers of 6 bottles, and cases of 24. In ShopSite, you would just have SKUs B1, B6 and B24. In the Order Manager, you would set up B6 as a kit consisting of 6 pieces of B1. B24 would have 24 pieces of B1. When you import your orders (or enter mail/phone/email orders manually into the Order Manager), the program will deduct the proper number of B1's needed for each order. There are other ways it could be handled, but that would be the easiest.
For more information, give us a call at 215-641-1837.