That only tells CherryPicking what device to start mining with and really has no use if your GPUs start with device 0. It's only useful if your CPU is identified as device 0. To add more GPUs, add a Miner= line in each pool .cfg for each GPU with the required mining credentials to mine on that pool. CherryPicking will use as many GPUs as there are valid Miner= lines. Note that I highly recommend having the same number of Miner lines in all your pool .cfg files.