Reports are surfacing that BMW may be changing their convertible options for the 1 and 3 series cars to be 2 and 4 series vehicles. You can read more about this breaking news on AutoBlog.
A site for BMW 3-series E93 news, experiences, and ideas. E93 designates the new model design for the BMW 3-series convertibles, including the U.S. 335i and 328i convertibles.
Reports are surfacing that BMW may be changing their convertible options for the 1 and 3 series cars to be 2 and 4 series vehicles. 
"Living up to the company's motto, this folding hardtop is a fantastic package for anyone who wants a BMW with "M" specs but who can't afford it." - MSN article
Of course, going with a quad exhaust requires some other cosmetic changes to the rear end of the car. The best look I could find is using the 92/e93 OEM M-Technik Rear Bumper with a carbon fiber rear diffuser. An example can be seen on the E93 at right; though, not with quad exhausts. The M-Technik gives the rear a clean look in my opinion, add quad exhausts and you'll have a very sweet custom change to your E93. Non of this is cheap when you add the $2,300 for the quad exhaust and about $1,800 for the M-Technik parts.