I'm in NorCal actually. Do you come across many Genesis' on the road down there and if so, any of them modified in any way?
I have the Magnaflow cat-back on my car and you will definitely hear it in the passenger compartment. There is a drone that you either love or hate. I've gotten used to the sound now but at first I wondered if I had made a mistake.
I've written in other threads that my installer suggested installing an X-pipe muffler called Tru-X from Magnaflow which essentially wraps the X-pipe like that which comes with the cat-back system into a muffler. This quiets things down particularly in the passenger compartment as the X-pipe is located just below while still providing the the exhaust flow benefit of the X-pipe. It's a 2-in 2-out muffler that would simply replace the X-pipe if you have one or the stock one which is an H-pipe if I recall correctly but I'm not positive as it's been a while. I still have it down in the garage. The cat-back itself uses a pure X-pipe. Here's a link to it if you're interested:
Magnaflow Tru-X Muffler
http://www.magnaflow.com/02product/shopexd.asp?zone=main&id=9386
You could just get the Tru-X muffler and a couple of universal mufflers with tips without buying the cat-back system but for the price of the cat-back versus the individual pieces, it was worth it to buy the full system. I got mine a ways back from Auto Anything for around $675 with Free Shipping. You will also get larger diameter pipes with the cat-back. Then you can just buy a Tru-X to replace the X-pipe that comes with the cat-back. Your only other cost will come from installation unless you do it yourself. I decided to have mine welded instead of using the bolt-on clamps it comes with for just a better, custom install and to reduce any exhaust leaks so it cost more for install.
As I've become accustomed to the sound, I haven't investigated making any change but a time may come when I do. I would hope that it would quiet things down a bit, especially the drone, while still providing a nice growl when getting on the accelerator.