You can't depend on the TV to send high quality audio from external sources to the receiver. For that you must run the audio directly to the receiver.
The best way to keep the receiver out of the picture is to use the TV for video switching and the receiver for audio switching.
You would have your DVD conencted as described in my second paragraph. Your HDMI equiped DVD player will most likely send a stereo feed to the tv over that.
As for other video sources, you would run follow suit, except thay you will need to connect an audio run (red/white RCA interconnects) to the TV.
Concurrently, you would connect the the best available audio to the receiver. Your cable box may (or may not, dunno) allow digital processing and, if do, you would run that to the receiver.
When you want to use the receiver for sound, simply turn the TV volume all the way down.