I am not aware of anyone using plywood in these applications. Not that it won't work, it just won't sound the same. If you want to try a low end solution, the usual recommendation is to go and get a 2 inch thick butcher block from Bed, Bath and Beyond
Wooden Platforms Redux
I asked in another thread about wood under components to eliminate vibration etc. I was steered towards maple and or walnut. Plywood of these two varieties will do, correct? Thanks, Mark