RX470 and RX480 requires 4GB system memory, so you just can't mine with 2GB.
That is right. You cannot mine with 2GB memory with the Claymore miners. You can mine with other miners for other coins.
Just received some RX470 cards and built a test Windows 7 x64 righ with just 1GB (ONE) of system RAM. It works just fine with 3 RX470 cards (soon receiving more).
The key is to use -gser 1 option to serialize card initialization and don't forget to change virtual memory to use 16GB paging file. I don't know if the latter is really necessary, but -gser helps.
Soon switching to linux for new cards.
BTW, can anybody point me to the explanation of Polaris power stage structure? I need to understand well what all those VDDs mean. AFAIK, main VRM supplies voltage to a controller that generates more voltages for VRAM, GPU, VRAM to GPU bus, etc. Also there is some offset (from what to what?) used to downvolt. I use them blindly but please help me to find an info about this, I want to optimize my system but like to understand what I'm doing.