your talking about 2 y pipes which will restrict the flow you are looking thus negating any gains.
your cars exhaust mods so easy! why not use some race cats in place of the secondaries to a true dual setup with a single dual inlet dual outlet magnaflow muffler. just past the secondary cats add a tube at a 45* angle exiting in front of the rear tires with the caps like the muffler. you can open them at the track.
also im having great luck with replacing the factory h pipe with a xpipe from magnaflow. killed the drone and deepened the sound.