Fivechannelguy: the results you found replacing the Gingko balls with Herbie's "MedicinBall"s are different than when I tried Herbie's 1-3/8 in. "grungebuster" balls. I found that the "grungebuster" ball diminished the liveliness and resolution of the turntable, creating a darker presentation. So I went back to using the stock Gingko balls. I did place two additional balls (more than recommended by Gingko) and that helped to both stabilize the movement of the top plate and provide a more airy, lively sound.
Perhaps the additional density/firmness of the "MedicinBall" compared to the "grungebuster" ball is why you found an improvement over the Gingko ball. It may provide a (somewhat) similar effect as adding Gingko balls. If I have some extra cash and want to experiment I might try the "MedicinBall".
Regards,
Tom