I Had the same problem with my 3803 to my Mac Amp
it turned out to be the cable. Make sure you have the correct type of cable and that all the trigger selections are turned on. The way the 3803 works is it only turns on the 12v trigger when one of the sources is selected that is set to on. so when you power up the denon make sure that the source that is selected has the trigger set to on.
I know you said you had all the triggers set to on but I just wanted to clearfiy it for you.
it turned out to be the cable. Make sure you have the correct type of cable and that all the trigger selections are turned on. The way the 3803 works is it only turns on the 12v trigger when one of the sources is selected that is set to on. so when you power up the denon make sure that the source that is selected has the trigger set to on.
I know you said you had all the triggers set to on but I just wanted to clearfiy it for you.