I've been down this road. First I had the B&B muffler. Terrible drone and too loud. I reduced the tips down to 2.5 (or 2.25) and that improved things very slightly.
Then I went to a Flowmaster (the B&B was cracking), and the solution for drone there was to cap one outlet. I used a Campbell's soup can with the end painted black. On track or fun run days, I'd just undo the hose clamp that held it on the exhaust.
Soup can:
Then I went to a Magnaflow muffler. No drone at any RPMs. I with I hadn't wasted my time with anything else. Mine might be slightly quieter because at the same time I switched to the 993 short headers from the B&B. But the Magnaflow seems to be MUCH better than the B&B or the Flowmaster. And I'm pretty sure it's the cheapest of the bunch, too.
Sounds SWEET.