You might also look at the Auto Poll setting on the 970 (pg 26 in the 970 manual). I've never seen your particular problem on my 970 but I know that when Auto Poll is ON it will switch from digital input to analog input when the digital stream is interrupted. If Auto Poll isn't OFF already try turning it OFF and see if that makes a difference. If it is OFF turn it back ON and see if that makes a difference. That might provide some clues as to what's going on.