My solution: The Empeg wasn't properly grounded. Hugo's response got me thinking and I found a much more solid direct-to-the-chassis ground point for the Empeg. That eliminated alternator whine.

That looks suspiciously (exactly) like what I told ellweber to do way back in the beginning of the thread. But everyone always comes back with: I know it's grounded properly, etc... 99.9% of the time it's the most simple problem. If I had a nickel for every time.....

Bruno