The mufflers aren't as much the sound as the H-pipe is. You will get nothing from aftermarket mufflers until you change to an O/R H-pipe. If I did my exhaust all over again, I would try MACs. I've done quite a few MAC jobs and they sound great. Right now, I have Magnaflows and they are sweet sounding, I just wish they were a little louder. If your going to get a pair of shorty headers, save your eardrums and DO NOT GET FLOWMASTERS.
Joe