I think you miscalculated. I'm almost done with the solution (it's actually taking me longer to type than to figure it out) Starting out with 2 coins on each side of the scale breaks the possibilities down nicely - 21:26:26. I have to stop for today, so I'm posting what I've got so far and I will try to finish it tomorrow.
If the scale is not balanced then let's say 1,2 is heavier than 3,4. We are down to 26 possibilities:
NO. (0) - there must be fakes here
1H. #1 or #2 (2)
1L. #3 or #4 (2)
LH. Either #3 or #4 is light and either #5 or #6 is heavy (4)
HL. Either #1 or #2 is heavy and one of the remaining coins #3 through #6 is light (8)
HH. [1,2],[1,5],[1,6],[2,5],[2,6] (5)
LL. [3,4],[3,5],[3,6],[4,5],[4,6] (5)