Here's something for the non-350 S550 owners: Roush Active Exhaust.
http://activeexhaust.roushperformance.com/
A bit spendy, but gets you customizable active exhaust note similar to what is on the GT350. Looks more flexible too, IMO.
This could be helpful for S550 GT owners going to a variety of tracks with/without sound restrictions (Laguna 90db vs. Thunderhill 103 or unlimited db, for example).
http://activeexhaust.roushperformance.com/
A bit spendy, but gets you customizable active exhaust note similar to what is on the GT350. Looks more flexible too, IMO.
This could be helpful for S550 GT owners going to a variety of tracks with/without sound restrictions (Laguna 90db vs. Thunderhill 103 or unlimited db, for example).