Charlie Watts likes solid maple drums, I think he has them made in Maryland somewhere. Could be the maple preserves the dynamics without screwing up the tone, as might be the case with other materials like MDF. Maybe NASA or someone should do a full blown dynamic analysis to see why maple is good for sound.
what is the theory behind maple stands and racks?
I have not "heard" a maple amp stand or rack - using Billy Bags products now, which are made from steel and mdf - but don't grasp why maple would be a good material to use - quite the opposite. Maple is used for some electric guitars because it "rings" - it is very dense and causes notes to sustain, which is to say, it continues to vibrate for a long time. This would seem to be exactly the opposite of what one wants in a stand or a rack. If there is some claim that vibration is "drained away", well, if the rack is continuing to ring, that would likely cause acoustical feedback - the equipment isn't isolated from the thing it is sitting on. Can anyone who is not a vendor of these things explain the why of it, or relate positive experiences that seem to have a basis in fact?