ing with this decision was a lesson in itself. Borla exhaust lesson
After much back and forth I ordered the Borla system 140353 for my 2011 SLS AWD from Amazon with 2 day shipping to the muffler shop for installation. I called Borla just to confirm that I wouldn't have the droning issue that I had on a 2009 Honda Civic Si. I sw Eric, cust service, he advises me that the system has been discontinued due to lack of sales and after checking with a coworker due to a design defect resulting in droning that may not be amenable to fixing. He very candidly told me to cancel the order and not to install the system. Needless, to say, I emailed Amazon but was unable to cancel the order. I spoke with the muffler shop asked them to refuse delivery. The muffler shop advised they can set me up with some after market mufflers that will accomplish what I want, a lighter, better sounding, freer flowing system. Interesting how all the back and forth grappl ing with this decision was a lesson in itself.
ing with this decision was a lesson in itself. 
Oops
It could all work out okay, especially with the the shop sounding keen to help out. You could end up with a very nice stainless system.
From my past experience the physically larger the muffler/ resonator size the better they work at reducing noise. You can also fit resonant chambers (like a T piece off the main piping) to filter undesirable frequencies- but I can't remember the correct name for them??? (It's the same idea as all the resonant chambers they hang off the factory air intake systems.) Even something like a reduced section of piping in the system could give a result you like. Just check what the shop is going to charge you for all the muffler/ resonator changes - I got caught out once with a custom system that was too loud..... it took about three muffler changes ($$$) before it was "satisfactory". In the end I discovered a major noise problem was from the system expanding in length significantly with heat- enough to make contact with the metal bodywork in behind the rear bumper!
From my past experience the physically larger the muffler/ resonator size the better they work at reducing noise. You can also fit resonant chambers (like a T piece off the main piping) to filter undesirable frequencies- but I can't remember the correct name for them??? (It's the same idea as all the resonant chambers they hang off the factory air intake systems.) Even something like a reduced section of piping in the system could give a result you like. Just check what the shop is going to charge you for all the muffler/ resonator changes - I got caught out once with a custom system that was too loud..... it took about three muffler changes ($$$) before it was "satisfactory". In the end I discovered a major noise problem was from the system expanding in length significantly with heat- enough to make contact with the metal bodywork in behind the rear bumper!
David