I only replaced the 2 rear mufflers and not the center muffler. I figured that could always be removed later on if it was still too quiet, but it's perfect the way it is.
I'm not quite sure what you mean by drone, but maybe exhaust resonating inside the car? It's audible inside the car, but not loud at all, and once I've reached cruising speed and am not accelerating the exhaust goes silent and can't be heard unless you give the engine more load with the gas pedal.
Yea, I've changed exhausts on many cars and sometimes you hear the exhaust in the cabin endlessly at certain speeds. It can become quite annoying. I suspect in your case the center muffler is playing an important part in eliminating drone. Thanks for your response and information. Based on your results, I'm considering changing the rear mufflers only, leaving the stock tips in place on my 4.6.