First off, I really like your wiring diagram! I've done many a sketch but nothing as pretty as your diagram and it really simplifies the process when you get behind your components with all the wires.

Second, there really isn't any video quality benefit of connecting the cable box to the TV via HDMI so I'd just use the component connection. As for sound I like the 5.1 on some TV programs so I keep my 990 in the loop when watching TV. If you don't use the Video 7 HDMI on your TV it will be available for a future BluRay player and you can use the 990's 7.1 analog inputs for audio.

Speaking of Blu Ray; if you get a player (you will need one with 7.1 output) get ready for making another diagram. I think I've connected almost every output on the back of my OPPO to the 990 or my TV. It is just as complex connecting a universal BD/DVD/CD player as it is wiring the rest of the system!

One question: Are you using a universal remote with all those components?

Have fun with your 990!