My only thought is if the "amp on" wire isn't connected properly would this prevent the amp from providing power?

That might do it, yeah. That's what happened with the install I did. I had to connect both the amp and antenna wires to the empeg's blue amp remote wire before it worked.

Of course, in that situation, it made no sound at all until the blue wire was hooked up...

Which plugs did you get with the OEM-1? There is a plethora of "A" and "B" harnesses available, which ones did you get?