My receiver, or maybe Blu-Ray player, confuses me. If I'm playing a Blu-Ray movie, and have the "bass out" on the receiver set to subwoofer, everything is perfect. If I'm playing a DVD or CD, and have the bass out set to subwoofer on the receiver, the subwoofer doesn't play anything. If I switch the "bass out" to "front" on the receiver, it still doesn't play anything. Only when I set the bass out to both does the subwoofer play anything. Why is this?