I wanna stack two Mono blocks but there is no rack that is sold with coasters. The rack is too small, etc. A wonderful market opportunity that no one takes an interest in.
Not true. Take a look at my very first post responding to your question. Sound Anchors makes wonderful, sturdy, sand-filled racks in whatever configuration you need, and they specifically offer two types of coasters that screw into the threaded inserts at the bottom of the racks. Many audio enthusiasts have used their racks to support amplifiers and other audio equipment for years. What more do you want?