"Sony/Phillips Digital Interface"
The 8886 supports 5.1ch S/PDIF output via the mic jack. You must enable digital output through the audio control panel.
Sager states in the 8886 manual: "Please use y-cable provided" however I don't believe any of us recieved that y-cable.
In any case, any 1/8" inch (or 3.5mm) TRS (stereo) y cable will work. It must be an insert type Y (stereo splitter). Normally, one end will be red and the other will be black.Here
is a link to a picture. Scroll down to model # YRA-154.
The 8886 will not output optical S/PDIF. It's a completely different technology with a completely different transmitter. The 1/8" type optical plug (like you'd plug to a minidisc) has a hole in the end to transmit the light, and the jack itself needs the transmitter to send the signal. Maybe the 5660 supports it, but the 8886 is strictly RCA-style.