“With regard to a wood platform or plinth, is it possible to make an educated guess as to the sonic effect between different hardwoods?”
>>>>All things being equal a thicker platform should perform better than a thinner one because it’s stiffer. Stiffness is required to bending forces, one of the isolation directions. Of a platform is used in conjunction with Springs the type of wood is not very important because the wood platform, as well as the component, is isolated from vibrations coming up from the floor. Also, any vibration that occurs on the wood platform, including acoustic vibration, can be easily dealt with by applying damping. Another variable is type of cones under the platform and under the component that is on top of the platform. How the wood is cut, with the grain or cross grain, should be audible. There is also the beauty of the wood to consider, e.g., Walnut, Maple, Cherry.