I discovered that adding a 5th board to my perfectly running Jupiter actually caused it to run at over 100Gh/s slower than having that 5th board in a separate miner (I have 2 Jups, but had to send 3 boards back for RMA). I know KNC stated that their system was supposed to be able to handle at least 1Th/s, but I've found this not to be true. It may just be a firmware thing though. The 5th board caused 5 Dies to not come online (low current issue) that otherwise work fine.
What firmware version were you running, and what power supply?