I've got a Yamaha DSP-AX750 recently. My sub (Kef 30B) has an on/OFF/AUTO switch. With my old sony amp I would leave it on auto and if sub was not getting anything it would go into standby (power LED on red). If it was getting a signal from the amp it would light green. I have crossover set to 120hz. My speakers are Mission Cinema 7 setup (773e Floorstander front, 77c centre, 77ds surrounds). I carried out auto setup, but noticed the fronts were set to small, so have changed them to large. Unless I leave sub in "on" position it doesn't trigger on.