OK, time to fix this mess.
Leave your cable box as it was. It was set up fine.
Did you check to see if your receiver was in stereo? If it was, it won't play all 5 speakers.
Use your optical cable to send digital audio to your receiver. Those other cables are regular analog cables and are not 75ohm stable.
Send ONLY PICTURE to your TV. Send ALL audio to your receiver.
Theres no need to send video to your receiver. Its just another cable needed for absolutely no gain.
If you want to use the DVI output on your cable box, you can get a DVI to HDMI cable that will work with your TV, freeing up a set of component cables for you DVD player.
If you want HD dvd, then you have to send picture to your receiver. But, it has ot be able to up convert. I am not familiar with your receiver so I don't know if it will work.
Wiring stereos it hard to explain over a forum, and it was very helpful that you had pictures.