Are you planning to enter sound off competitions? Would you honestly know any different if the sub is in a slightly smaller box? Unless you are an ICE guru, who really knows what they are talking about (which from the looks of things, you are not) then i wouldnt worry about 6 litres of space, im sure the sub will still sound the dogs danglies to you. I think my sub is in the wrong size box, but i dont give a monkeys, it sounds great to me.