Putting duals on the V6 4.0L is more for visual than it is for performance; you won't get much if any gains out of the V6 from exhaust work. Also, don't expect miracles in the way of a deep exhaust note from the 4.0. You can deepen it a bit but it'll never sound like a V8.
Many folks will put a GT passenger side takeoff (manual GT preferred) in place of their OE axleback. It's a bit deeper than stock but not by a lot.
07 GT Prem: Alloy, MT, 3.55's, Steeda CAI w/Brenspeed tunes, FRPP Stingers, 275/40/18 Goodyear Eagle F1 A/S on SVT Cobras (OE GT500's), 14" shorty, Wheelskin side scoops & qtr window louvers, A-H rear window louvers, SHR honeycomb blackout panel, Sequentials, Hella Optilux Extreme XY fogs, Silverstars
06 V6: Legend Lime, Pony Package, 14" shorty, Sequentials, Hella Optilux Extreme XY fogs, Silverstars