Yup, the stock sound is pretty good - just not loud enough IMO. So, I've been kicking around the idea of going with an offroad MAC Prochamber instead of changing out the mufflers. Only problem with that is then you have to get a computer tune and there are also issues about having to put the stock piece back on any time you need warranty service... etc.
I guess I'm not certain. People are now finding that it might not be necessary - you will need to do something about the rear O2 sensors though. If one could get away without getting a tune, I'd do it.
When getting your car inspected just say that the prochamber is a high flow cat, thats what my cousin says and he gets away with it.
IMO both Bassani and Flowmaster sound good on the 05, but as far as quality Bassani is head and shoulders above Flowmaster. That said they make completely different sounds.
IMO the clips of the Corsa axle-back on the Corsa website sound really awesome. However, there seems to be only one person on TMS.com that installed them and he didnt like them. They sound good on the site though. http://www.corsaperf.com/mustang.htm
I'm not worried about the inspection - we don't have to get it inspected where I live. I'm only worried about the dealer seeing the offroad exhaust when I take the car in for my strut popping and radio TSBs.