My car middle silencer box has quarter inch hole (made by gear lever hitting) and rear box also has half inch hole (rusted). It makes such a balanced sound that many people, despite of having good sports mufflers ask me from where did I get it :D.
Either spend around 3000 for sports muffler or DIY (mentioned below).
Drill one small hole in rear box, start by quarter inch. If that does not work, make quarter inch multiple holes 2, 3, 4,...... until you get your desired results.
Note: Do it at your own risk, just sharing an experience.