BUT, he said that the Empeg doesn't go to standby or power down when the ignition is turned off.

If you look

here
and
here

I think you may find, not the answer to your problem, but some information about what is causing it.

Don't be misled by the beginnings of the first thread - even though you aren't getting the "thump" it talks about, the thread does develop into topics relevant to your situation.

tanstaafl.

"There Ain't No Such Thing As A Free Lunch"