This message was posted on behalf of Intel Corporation
I did a little research and I'm afraid to tell you that it isn't possible to increase the PWM source current of the Edison boards internally . Personally, I would recommend you to use an external PWM controller to implement your flight controller, if you want an example that uses Emax simonk 12A you can check this thread: https://communities.intel.com/message/292004#292004. The controller used there can help you with your current issues and PWM resolution.
I hope this information helps you.
Thanks for the feedback Leonardo! I was able to make a simple circuit consisting of a transistor and the 5v source which allows me to use the pwm lines to spin the motors. I can do so at 500 hz pwm rate, and get about 75 discrete pulse width values between the min and max speeds of the motor. This may be enough for stable flight but If not I will likely buy an external pwm controller as you suggested.