I have a Pioneer surround sound system (Xbox 360 edition) that has 2 optical (toslink) and 1 coaxial inputs to handle 5.1 digital sound. It also has basic L/R RCA Analog connectors for basic stereo input.
My Mac Mini and my Xbox 360 are using the optical inputs. I have only a Coaxial and an Analog stereo inputs left.
So what I did was add a Coaxial digital connection to my PS3 Slim. It is much easier then it seems.
Basically, the optical (toslink) gets digital audio from the motherboards audio system and turns it into light pulses which gets turned back into audio in your receivers optical connection. The toslink's positive and negative solder points can accept a standard RCA female connector soldered to it.
Unfortunately, I'am not able to post pictures here but I can describe the mod easily.
Find any teardown tutorial of the PS3 Slim. You can ignore the fine details and just find the quickest path to the bottom of the motherboard. Once the motherboard's bottom is exposed you have to locate the toslink connector's solder points. With the toslink connector facing up and away from you, you will see three solder points. The left most solder point is the positive, the middle is not used, and the far right is the negative (same on most devices). Prepare your RCA connector. Solder your wires to your Female RCA connector (middle pin is positive and outer shell is negative)
Then solder the wires to the motherboard in the right order (positive=left, negative=right). I drilled a 1/4 inch hole in the back of the PS3 case between the serial number sticker and the LAN connector and installed my connector. I tested it and it works perfect.
You can even use the toslink at the same time if you have a need to.
Tip 1: When you take the heat shield off the bottom of the motherboard you will have to remove the spring loaded metal bands that put pressure on he CPU/GPU's and their heat sinks. When you do so you do not have to remove the heat sinks. Just leave the motherboard upside (bottom up, heat sink down) on the work surface without removing the heat sinks, that way you won't have to repair or replace the thermal paste.
Tip 2: When preparing to solder your Coaxial connector, leave about 5 inches of wires so you can reassemble the PS3 without pulling on the soldered wires.
Tip 3: Before drilling your 1/4 inch hole in your PS3 case place the motherboard loosely back in the bottom case and judge where you can install your RCA connector. I made a mistake when I drilled my first hole and had to drill another hole just a little over to fix the problem.
If pictures are needed then perhaps someone can suggest how.