Granite Slabs

Just trying to figure out if I want to get my speakers off the carpet with spikes onto a platform of some sort. Not sure which is a better sound/solution.

Get a nice wood maple and put spike.

I would invest in Townshend Podiums for your speakers. Virtually everyone that has gotten them has been stunned at the performance increase, including me. No amount of greater mass is going to do what the podiums do. 

I have used granite under components... it must have vibration isolation or it will simply transfer the ground vibrations directly from the floor to the speakers and will accomplish nothing. Granite rings... and is an exceptional conductor of vibration... unlike something like Black Diamond Racing platforms. So you can use it... but it requires careful thought. 

Yeah, granite will not completely isolate, but may transfer less noise than a suspended wooden floor.  I’m not sure how much extra isolation you need with 200 lb speakers on the floor.  Nothing is perfect, but perhaps a minus K platform is closer than most everything else.