Low racks behind speakers is great upgrade over taller stands, my setup all spread out over 13' wide room, nothing more than 19" tall. What is between speakers greatly affects sound staging and imaging. I was never able to fully lock in center image with tall equipment stands there, reflections all over the place makes for confused sound stage. Diffusion is what you want between speakers.
As far as equipment racks, I use a concrete fireplace hearth underneath diy sand boxes made of birch ply topped by 1/4" aluminum plates with built in vibration absorption sinks. Equipment footers various ball bearing devices or nobsound springs.