A lot of S55 guys think downpipes are the recipe as well but making it louder doesn't make it sound better. Here's an X3M with catless downpipes, which sounds way worse than stock IMO:
Again, I'm a huge fan of S58 and can't wait to grab a G80 once it's available but there is no aftermarket exhaust/downpipe combination that will make it sound remotely as good as the AMG.