GP111 is basically unusable right now, as is SPI CS 1, because of the built in support for the ADC over SPI for the Arduino board. Sadly, the driver that runs the ADC does not get out of the way when the ADC is not being used or detected blocking everyone from using those pin/interfaces for something else. To top it off, everything is baked into the kernel making fixing this problem difficult at best. In short, I hope the routing is not difficult to change.
Little side note, do some research on I2C 6, I may be remembering wrong, but I may have seen somewhere that it doesn't exactly work and that I2C 1 should be used. Again, not completely sure, just trying to save you from more headaches caused by the half-baked-ness that is the Edison.
Thanks for the solid insight.
With guidance, I've been using I2C6 successfully.
One of the I2C issues is: I2C1 is the mux system for the Arduino board and I2C6 is the one available in the header. But... if you buy something like Sparkfun's 9DOF board, they wired it to I2C1 which means you can't program it using the Arduino IDE. You have to edit the board header file to use it.