Find the various manuals and read them.
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Keeping in mind this is just an analog Dolby Pro Logic receiver, there are limitations to what it can do sonically. Dolby Pro Logic is NOT 5.1 as I'm sure your DVD and possibly Cable Box are capable of producing.
KM-106 is just a power amp. No mysteries there. Feed it something, attach speakers, duh.
What did you plan to use it for in this scenario? If you want to slave it or drive a separate passive subwoofer with the Fisher as the central control, the best you can do is borrow analog stereo Line Level out from the unused Tape 2 or Video Out, but don't actually select them on the front panel. THAT would disconnect whatever source you were listening to. And you WONT have local control of the volume as you would with a real AV Receiver.
Sony DVD player (what model?). RTFM. I'd just run audio from it to the Fisher and Video to your TV, unless you want ONLY composite video quality.
ADC-SS2: See Figure 5 in the Fisher manual. Hook it where they show the cassette deck, using Line In and Line Out of the SS2. If you want to use a Tape Deck or 2 attach them to the SS-2 in its Tape loops.