If I read your post correctly, you have your subs inputs connected to the high level amplifier outputs that connect to the speakers, and you have tried connecting the subs to  the amp outputs as well as at the speaker inputs.  Correct?

I assume the subs are active and you have them set to auto-on.  Correct?

With the AVA amp there is no problem.  I assume that is true no matter what position the chassis ground switch is in on the back of the AVA amp.  If the switch did make a difference it would be telling us something.

My best guess is that the Decware amp output, which is transformer coupled with neither output grounded, is being "seen" by the subwoofer amp as not off...its probably picking up a small amount of induced noise, probably 60 or 120hz.  The subs stay on because they see a signal and they amplify it.

So, if that's the case, you could turn off or unplug the subs when you turn everything else off.  Or you could try grounding one of the amplifier outputs on each channel.


Dan