You want it to sound somewhat like an SRT4...either buy one, or turbo your car. It's N/A right now so it's much easier than having a Supercharged car.
Also; no SRT4 sounds like a Boxer. It sounds like a boosted four banger with a cat coughing up a hairball. Been around plenty. A boxer sounds like a boxer. If you want to make your car sound crazy different, then have someone make un-equal length headers for you to simulate that boxer noise. And I'm sure making them from scratch will cost more than what your car is worth. A guy makes them for the N/A Ecotec's and they actually robbed HP/TQ at points all over in the power curve along with not fitting well...and costing six times as much as your everyday header that WORKS.
So if you want more noise, get the 2.5" catless downpipe...and cam the thing. That'll give you an idle worth caring about...but it's still a 3800, so when you rev it...it sounds like ass.