The key to eliminating tt rumble is 3 things...Isolation Isolation Isolation. You simply cannot isolate enough. Mounting a tt on an exterior wall away from the speakers usually does the trick. I have had great success with this in addition to using Sorbethane cones under the shelf and used cork isolators under the tt feet. I am also big on short as possible speaker cables and long runs of "Balanced" interconnects. I have monoblocks and have used this method for years without fidelity loss of any kind.
Good luck
Good luck