I don't mind answering your questions as long as you don't mind answering mine as well.
(1) There should be no reason to have both analog and HDMI coming from your DVD player as SACD can transfer over HDMI. Why do you have both connections?
(2) Your current Comcast connection directly to the TV is fine as long as you don't ever want to use the surround speakers, although I'm surprised you wouldn't use them for movies at least by connecting an optical cable from the box to the 2807. If your box is a HD cable box you would be able to pass DD 5.1 to the surround speakers and even if it's simply a SD box, the 2807 would still use DD PLII to simulate 5.1 surround through your speakers.
(3) You do need to address each source if you're not using the default connections that the Denon 2807 has already set up. HDMI, component, and optical connections are assignable whereas the composite video and RCA audio are not which is why you must use whatever source name you have the Wii RCA cable plugged in to for your Wii source name.