I looked at the pinout of the Focusrite ISA One DB9 S/PDIF RCA adapter cable.

Essentially, it does 4 +/- (8 wires) and a ground (1 wire); It has 4 rca coaxial plugs one per +/- pair connected.

But the ADC on the ISA One only supports a single s/pdif or aes out (stereo); why is this?