I would be most interested in your feedback. The Quad rear vs Quad side exhaust is most interesting from a comfort and noise level in/out.
The Quad rear option is probably the Aero Racing system which I have on my car. Admittedly, mine is a 'Max rather than a Coupe but I presume that, as a fixed-head, the exhaust will sound the same as in a Coupe.
I found my original twin pipes too anodyne - they didn't sound that special. The Aero Racing Quad pipes sound very fruity with large throttle openings and have a nice rumble at tickover, but when you are just cruising (which in an auto will be at 1200 - 1800 rpm) you can easily hold a conversation, use a blue-tooth phone etc without the exhaust noise intruding.
However, a drawback of rear exit systems (twin and quad) is that there is scant ground clearance where the exhaust mid section 'elbows' to skirt the rear suspension. Because the exhaust tips are welded to the back box, fettling the rear hanger so that the back box and the elbow sit a little higher is easier with the single tips system because the twin tips will not sit level if the back box is raised too high.
Of course, side exits neatly avoid clearance problems, but shout 'racer' rather than 'grand tourer' (which may be exactly what you want...). On other cars I tested, I found the side exits noticeably LOUDER in the cabin at cruising speed.
