I have a suggestion for your centre speaker that should cost almost nothing. If the depth of the centre plus the depth of the TV base don't exceed the depth of the cabinet, how about placing the centre speaker in front of the TV. The speaker will probably obscure the bottom of the TV screen, so you just need to lift it a few inches. Some pieces of 2'"x4", painted black, or wrapped in black fabric would do the trick. That's about as simple as it can possibly get. If you consider that a bit too "ghetto", you could go a bit further.
You're centre is 7" high. Get a small piece of 3/4" MDF or plywood, approx. 30" wide by 12" deep. Glue pieces of 2"x8", on edge, to the ends of the MDF/plywood. You now have a stand that sits above the centre speaker, where you can place you're TV. Using MDF or plywood to make the whole thing would look nicer, but you'd probably need to brace the corners.
Just a suggestion. But, I guarantee that getting that centre off the floor will improve the sound quality enough to justify the effort and expense.