Denon 2900 Analog outputs...?

On the back of the 2900 & 5900 there is eight total analog outputs, but the first 2 sets are confusing to me... the are FL1 FL2 FR1 FR2. Which two are for the 2-channel SACD? and if the FL1 FR2 are for SACD DVD audio, etc..
why do you need the FK2 FR2 for a six channel system when you already have the main speakers taken care of? hope I made myself clear...
The front-left output is in parallel with the left output, and the front-right output is in parallel with the right output. A full set of 6-channel outputs are provided for driving the 6-channel inputs of a pre/pro/receiver, and a stereo pair is provided for connection to a stereo (2-channel) system if one wants a separate connection.