I've had true duals for well over ten years. I don't need a crossover and don't even want a crossover. I don't know why you say that.
Does your car have an exhaust going from each cat/header straight to the back? If so, you're actually losing some power, since the uneven pulses of the V8 are required for proper operation of any v8 engine with a cross plane crank. Are X-pipes and H-pipes Better Than Straight Pipes on Dual Exhaust Systems?