Cool, but you do understand that half of your "secret sauce" efforts are non scientifically sound without empirical data, so I'm guessing you just tried this out and lucked out! Engineers tune exhaust using CAD flow analysis and modeling software, and run experiments to verify results. Adding a hollow chamber adds volume to your exhaust piping, which can amplify or dampen certain exhaust frequencies. F1/Gallardo sound claims don't make sense since those engines are flat-crank, which gives them that specific dual-frequency sound (ala F355).
But, to make the S54 free flow, yet not sound "rice", is not easy, so it is great that you've gotten close with minimal efforts!
*Edit: I just realized it still sounds like a honda!