You have to turn off Auto Poll. This is described on page 26 of the 970 manual.
Note that you have to do this for each input. You may not want to do it for TV if your box has some channels digital and some that are only analog-you'll have no sound on the analog only channels. If all you TV channels have digital sound it should work just fine.
This cleared up pretty much all of the dropout problems on my 970.
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975/7075/SMS-1
Aperion Verus Grand Towers & Bookshelves, Verus Forte Center, Infinity Surrounds, Ultra-X12
Oppo BDP-203, XBOX360, Xbox One
LG 65" OLED
RR2150 w/Klipsch SCR-2