Oops, sorry, so there are definitions for the pins, I must have missed it because those lines where commented out. So I guess those are the default pins because their definition is commented out?
So if I got this right, I need to declare 2 more pins for the other pot. The SPI_CLOCK is the same for both, and the SPI_CS is also the same since both pots are single-channel. Something like this maybe? (Pins 11 and 12 for SPI/SPO on pot 1 and pins 6 and 7 for pot 2)
#define SPI_CS 10 //arduino <-> SPI Chip Select -> CS (Pin 01 on McpDigitalPot DIP)
#define SPI_CLOCK 13 //arduino <-> SPI Slave Clock Input -> SCK (Pin 02 on McpDigitalPot DIP)
#define SPI_MOSI_1 11 //arduino <-> SPI Master Out Slave In -> SDI (Pin 03 on McpDigitalPot DIP)
#define SPI_MISO_1 12 //arduino <-> SPI Master In Slave Out -> SDO (Pin 13 on McpDigitalPot DIP)
#define SPI_MOSI_2 6 //arduino <-> SPI Master Out Slave In -> SDI (Pin 03 on McpDigitalPot DIP)
#define SPI_MISO_2 7 //arduino <-> SPI Master In Slave Out -> SDO (Pin 13 on McpDigitalPot DIP)