I think where we're getting confused is the part where you mention "optical RCA." There is in fact no such thing. I would like this straightened out once and for all, so I'm gonna make this more complicated than it should be and then post my question at the end. I'm not trying to condescend to anyone, but I want to make it clear exactly what we're trying to ask.
There are two types of sound output that computer systems typically use. One is analog out (which is output from a standard headphone-type mini-jack and contains sound information stored as an electrical (but not digital) representation of acoustic waves. The other is digital out, which represents sound information as 1's and 0's. This digital signal can be sent in one of two ways: electrically or optically. If the digital signal is sent electrically, it travels through a standard RCA cable (with the same end connector as a composite video cable). If the digital signal is sent optically, it is represented as a pattern of light flashes that travel along a fiber-optic cable (very different from an electrical cable, it allows virtually lossless transmission of light as opposed to electricity) to a special connector called Toslink (it is square shaped and the female jack generally has a special protective guard that is removed to insert the cable).
The two pictures on the left above show a Toslink connector from different angles while the one on the right shows two RCA connectors. The output jack on the 8886 is a standard mini-jack (what you connect your headphones to on a portable MP3 player). So, you need an adapter to use either of these.
The adapter on the top converts the output from the 8886 to RCA, while the one on the bottom converts to Toslink, but many computers that output digital sound do not support the latter. The signal that is transmitted using either is the same, so why does it even matter if Toslink is supported? Well, people often complain of interference in the audio system of their computer, and audio that is sent optically is largely immune from electrical interference from other components of the computer.
We know that electrical digital output is supported as it is mentioned in the manual and an adapter is included with the system. So, the question is: Has anyone used a mini to Toslink adapter to output a digital signal optically from their 8886? Or, can anyone confirm that it is possible?