Steve, Rob(Argon)has a similar thread about his reluctant EP500 in the Advice forum, which you might take a look at. I take it that the original sub amp didn't have this problem and I wonder if the new ones have a higher input voltage threshold to turn on. The first thing to try is setting the sub trim on the receiver a few points higher to increase the voltage output and make it more likely that the sub amp will "wake up". The volume control on the sub should be decreased proportionately so that the overall sub sound level stays the same.
