I called Magnaflow and asked them the best location to install their Tru X-Pipe... and this is what they say to do:
Where the 2 exhaust pipes come together on the passenger side, place a 2 to 3 foot strip of masking tape down the length of each pipe.
Start the engine and let it run just long enough to start to burn the masking tape.
Take a look at each pipe to determine where the tape burned.
The Tru X-Pipe should be installed half way between each burned area to equalize the exhaust. If the tape burns in the same spot on both pipes, install the Tru X-Pipe there.
I hope this helps...