How can I emulate two analog joysticks (potentiometers) with an Arduino?
The Arduino can talk to multiple SPI slaves. Not at the same exact time, but faster than human reaction times. Each SPI slave has its own CS (Chip Select) pin, which when driven low, activates the SPI interface. One Arduino digital pin per chip. Then all the SPI Pots will use the same SPI bus pins. Your sketch would require that you toggle the Chip Select for each Pot separately, before you send data through the SPI port.