Do you mean the standby HDMI passthru, or the regular standby light when you turn the receiver off?
If its the second one you'll need to unplug your receiver for that to happen. That would be a good test, unplug your receiver from the wall and see if your Def Tech sub shuts down.
I can't believe that would be causing the problem though as i've had multiple Denon/Marantz receivers and any sub I've used with an auto switch will turn off after a short period of time of not getting a signal.
Maybe the HDMI standby pass thru is causing other outputs to stay on too. But the subwoofer out is analog so it should shut down when only HDMI passthru is working.
Last edited by afrogt; 06-14-2014 at 08:45 PM.