sounds like my 99 sls with the magnaflows i have had them on for about 3 weeks ther were quiet at first and I was pissed so I put on a high flow cat and removed the resonator and im lovin it I didnt want it too loud but I wanted people to notice it and belive me they do!
I just put some 50 series flowmasters on my 05 STS v8. They sound great and I think they will give you what you are looking for. no highway drone, quite driving around, and loud when you get on them. Make sure you get the 50 series and not the 40 series. I had the 40 series on my 99 STS and they had a drone and were too loud.
I did my 05 STS for $300 installed.