I like the fact at 50 MPH the only thing I can hear is some slight wind noise or a stepper motor.
The ever so familiar sound of a V8 exhaust note happens the way it does mainly from the nature of not only of the motor, but the plumbing. The I6 has an exhaust pulse that follows each other like a trail of kindergarteners going to lunch, all down one tube.
The V8 has a rap from one side and has a lengthy travel to the junction, then the same on the other side. Nice long tube, lots of echo, lots of everything that makes that thumping exhaust note. Doesn't matter if it's a 4 cyl, I6,, the buzzsaw pulses won't change. I'm going to bet that having 2 exhaust valves may even play with the note as opposed to 1 larger one.
Andy, if I was going to add some bass and character to this exhaust, I would probably get a high flow cat with a larger opening, branch it off to 2 short mufflers...prob a pair of Dynomaxes or similiar, then right into the resonator or a pair of resonators if they would fit before the axle. Then a larger taillpipe to aid in the scavenging of the cooler exhaust.
This is what I want to do later but with a single res, i'm looking for a muffler that will fit with the resonator keeping them together but not having the res poke it's nasty head out behind the axle. A nice clean 2 1/2" or larger tailpipe would finish it nicely.
A custom set of long tube headers would help but not much, basically you will be changing the pitch or tone of the buzzing I6 note and won't sound much better than a BMW M3 with the I6..which has wicked R&D involved.