Hey,

First of all try to start from a fresh install. Add one graphics card at a time to let Windows recognize the card. After it is recognized shutdown and add another card and repeat the process. I read this in another thread but this person added the cards in a specific order; PCI-E 7, 6, 5, 1, 2, 3.

When the 6th card is detected with the code 43 error use the 13.1 drivers from techpowerup.com. Hopefully, that fixes your issue connecting all 6 cards.

I read this from another thread so not sure if it is 100% but this guy made it work with the same mobo. Here is the link to the thread [https://litecointalk.org/index.php?topic=5086.0]