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.
For voltage, I just change the state 7 (boost). PowerColor Red Devil doesn't like you changing voltage for some reason, but Sapphire Nitro, and an ASUS card are fine. Stock voltage varies from like 1070-1150. Out of 11 cards, 1020mv has always been stable, some cards will go down to 955mv (1260MHz core) and be perfectly stable. Check ASIC quality in GPU-Z, generally the higher this is, the less voltage is needed. You can keep lowering voltage until system lock, then add like 40mv if you want a quick way to find ballpark estimate lowest stable (some cards you need to stop miner between changes, press 0-9 on miner).