@Zaigoukyou, hmm I don't know if you can add it like that. I know that the kyuubi is the strongest one. But you can't say that he is 9X stronger than the onetails.
Also, going by your logic, you can say that the Juubi is acutally missing at least 2/3 of the tailed beast's power since 1/2 Karama was able to tie 6 tailed beasts, that way more than 9 tails. So yes, you're right, the Kyubii is much stronger than the combined might of the tailed beasts that when into the Juubi. But the 7 bijuus that went in was merely the keys to unlocking the Juubi. It's like in DBZ when Imperfect Cell absorbed 17 and 18. Perfect Cell is way stronger than both 17,18 and imperfect Cell combined.
The key point is that adding the remaining two is merely the key to unlocking the Juubi's full strength, whatever it is. But you can't say that it's Current Juubi+8tails+9tails=Complete Juubi. It doesn't add like that. The result could be more, it could be less.