I think the 4.8 sounds great as is and i wouldnt mess with it unless you replace the whole system. The next thing io would like to do is have the car lowered a touch but even that really isnt that bad i think it already sits around 1-1 1/2 lower than the 4.4. My garage wont do it via DIS dont ask me why but they wont so i my look at the Intrax suspension module.

You might also want to check the wall thickness on the pipe you got to replace you resonator. If it is not thick enough it sounds like shit. it happened to me once with my 88 M6. I put on strait pipes to replace the resonators and they were cheap pipes. But i figured a pipes a pipe. Well it sounded like shit. Then i went to a better mechanic and he said it was coused buy the pipe walls being too thin. He said i will get you some that are the same thickness as oem and it should solve the problem. so we wnt ahead and it sounded great. so that might be your problem too.