David, all of my experiences have shown that the less "soft" material under the TT, the better. Preferably none. Hard materials that control vibration would be preferable to soft in a TT application. I strictly steer away from rubber, springs, air bladders, sorbothane, and the like in my personal TT support. I have always found rigid stands with good solid direct coupling to the floor have always served me better, especially in terms of bass and dynamics. Different people have different needs and tastes, but that is what I have concluded. It was better on all my different kinds of TTs, in different houses and rooms. However I don't play at 117db, so that could make a difference. Up to 108db, I have found no ill effects from this type of setting.
As far as adding more weight to the stand, that would be individual to the turntable in question. It will certainly change the vibration characteristics of the stand, and it may be better or may be worse. My guess that with a TNT it might be a little better to have more weight, but I'm not certain about it.
