did you check the amavisd-new web site? http://www.ijs.si/software/amavisd/#faq-net-server
you know, I did read that too, but I never had to jump through that hoop on a nearly identical machine. I applied the new subroutine to the new box, and it solved the issue.
I have *no* idea why it's actually working on the other (old) box. I vote for "voodoo."
:)
I also updated my Gentoo forums post to reflect the fact that "/usr/sbin/amavisd reload" is the recommended method for bouncing the daemon, and "/etc/init.d/amavisd restart" just pukes on itself.