I was also bogged down at this point - and in fact the EDI did not see a cu.usbmodem.
The actual issue was a dodgy USB cable - although the cable worked fine on an Arduino Due suspect (cheap chinese cable) that it was a bit dodgy.
Ran blink fine.
Ran the Prime number test which took (from memory 1760 msec) on the Due and it took 11 msec on the Arduino Edison......................
Stan