I actually found an easy, real fix for the problem, purely by coincidence. :))
It only works if you have an Airport Express configured with an external speaker setup.
1. In the iTunes window, switch the output from "Computer" to the Airport speaker.
2. Then switch it back to "Computer". Volume Logic will then work again.

It can, of course, be used with Airfoil to transmit the processed music stream to the external Airport speakers, since iTunes does not otherwise allow any processing apps to be switched in between itself and the Airport output.

Hope this helps!