only so much you can do with a non luxury car. Eventually your tires are going to wear down adn it will be a bit louder again, so for now enjoy it

just turn your beats up and ignore it lol.
Sorta off topic but i remember seeing a thread where a guy bought a acura csx type s (or was a civic si), and he removed his dash to take the insulating mat under for "weight reduction", aside from him being an idiot, i remember in the pics that the mat thing was THICK as hell. Hence why I think it was from a acura. But yeah higher end cars focus more on that stuff so I would say your best bet would probably be to dynamat your whole car.
It would help with your SQ sound system but then you also have down falls of costs, time (time = money), extra weight, therefore mpg will decrease etc etc.