There is nothing you can do unless you connect the display to 8 GB or 6 GB card. As this isn't possible in your case, you can instead run separate instance of PhoenixMiner for just GPU1 (adding the argument -gpus 1) and use a pool that only mines ETH. The other five cards will run on another instance of PhoenixMiner (with -gpus 23456), that can mine both ETH and ETC.
How to make this? With a 2 bat files? I will have 2 miners on the screen or is it possible to make in one?