When you do it and maybe just mock up the Center sitting on the subs, have a look at either "end cap" for the center. I think it's closed on both sides, right? You could make / buy / think of idea for "brackets / mounts / legs" that attach to the left and right end cap of the center. You can install threaded nutserts and make it so it's not permanent, in case you needed to use stand again, etc. If you get really slick, you can make the bracket so that it's adjustable, you can tweak the up / down angle, if needed.
In other words, "What can I attach to either end so I can sit the center on a flat surface and at proper angle... without the big stand?" There could be some cheap little brackets on Amazon, or go brainstorm at Home Depot... it bet there is some little thing to discover to make that super easy.