The suggestion, coming from G401fan, Prem and others to replace the marble rack top has turned out to be one of the best investments I've made. I got a 3" x 65" x 20" Maplewood top made. It has worked wonders. I won't say that the sound is brighter or warmer, but the focus, soundstage and imaging have improved quite dramatically. And a very rich tone, not just from my TT, but from all my sources.
The CDP, TT and Power amp are placed directly on the Maple top. No isolating feet. Other components are on lower shelves, which are made of Beech wood.
Thanks again! The suggestions were invaluable.