Eric, the Masterlink signal only carries data, voltage switching (-7 to -15V on pin 11 and +7 to +15V on pin 12---down to -+3 on standby respectively) and balanced audio. The audio is on the following pins, all with Resistance in of 2.2M Ohms, and Resistance out of 75 Ohms at 1V balanced:
Pin 13: minus Left
Pin 14: plus Left
Pin 15: minus Right
Pin 16: plus Right
I believe that an early version of the ML cable (with four rather than three twisted groups of three) may have been designed for video, but today's ML system relies on a 75 Ohm coax connection back to the main splitter for video distribution.