If you have the cable boxes hdmi cable running to the onkyo then yes you need it on to watch cable. Another option would be to run the hdmi cable to your display and also run a digital audio cable to the receiver so you can watch cable without the receiver on but if for some reason you wanted to watch cable in surround you could also turn the receiver on.
Exactamente dude.
That's why I stayed away from the "video-switching" receivers initially. I didn't see the point of turning my receiver on just to watch TV. But now with my 661 I have my PS 3 and DVD player going to the receiver, since I wouldn't watch those without my receiver, and I have component cables going from my cable box to the TV and an optical cable going to the receiver, so I can have sound from my stereo if I happen to be watching a concert or sporting event on cable.
Works great.
So the 805 is finally out?!?! Cool. That's what I was going to get initially, but I got tired of waiting. How do you like it so far?